diff --git a/README.md b/README.md
index 1a4d0cd..71ea5f9 100644
--- a/README.md
+++ b/README.md
@@ -118,6 +118,8 @@ On launch, gclo shows a brief branded splash, then the **Quick Sync** connect ca
 
 **Activity log:** View > Activity log… shows the tail of today's log and links to the logs folder. Logs live under `%LOCALAPPDATA%\KofTwentyTwo\gclo\logs`, one file per day, kept for 30 days; they record run parameters and per-repo failures and never contain your token (see [SECURITY.md](SECURITY.md)).
 
+**Share:** Help > Share gclo by email… opens a new message in your email program with an invitation already written: what gclo is, where to download the latest release, and how to install it. Type an address and send; gclo itself sends nothing. If no email program is set up, the text is shown and copied to the clipboard, to paste into a message by hand.
+
 **Updates:** Help > Check for updates… downloads and applies the latest release for your channel. Self-update is only available in installed builds (not the portable zip or a local debug build).
 
 ### Saved accounts
diff --git a/gclo.Engine.Tests/ShareInvitationTests.cs b/gclo.Engine.Tests/ShareInvitationTests.cs
new file mode 100644
index 0000000..c69d800
--- /dev/null
+++ b/gclo.Engine.Tests/ShareInvitationTests.cs
@@ -0,0 +1,161 @@
+/*
+ * Copyright (c) 2026 James Maes (KofTwentyTwo)
+ * SPDX-License-Identifier: MIT
+ */
+
+using gclo.ViewModels;
+
+
+namespace gclo.Engine.Tests;
+
+
+/// <summary>
+/// <see cref="ShareInvitation"/> writes the email behind Help &gt; Share: what the app
+/// is, where to get it, and a link a mail program opens with everything but the
+/// recipient filled in (#163).
+/// </summary>
+public sealed class ShareInvitationTests
+{
+   private const string Repository = "https://github.com/KofTwentyTwo/gclo";
+
+   private static ShareInvitation Invitation() => ShareInvitation.Create(Repository, "1.2.3 (abc1234)");
+
+
+
+   [Fact]
+   public void TheBody_SaysWhatItIs_WhereToGetIt_AndHowToInstallIt()
+   {
+      ShareInvitation invitation = Invitation();
+
+      Assert.Equal("Try gclo: clone and update every repository of a GitHub organization", invitation.Subject);
+      Assert.Contains("clones every repository of a GitHub organization or account", invitation.Body);
+      Assert.Contains(Repository + "/releases/latest", invitation.Body);
+      Assert.Contains("gclo-stable-Setup.exe", invitation.Body);
+      Assert.Contains("scoop bucket add gclo " + Repository, invitation.Body);
+      Assert.Contains("scoop install gclo", invitation.Body);
+      Assert.Contains(Repository + "#readme", invitation.Body);
+      // Filing an issue needs an account on the project's server; the message does
+      // not send a stranger to a sign-in page. They answer the person who wrote.
+      Assert.DoesNotContain("/issues", invitation.Body);
+      Assert.Contains("tell me what you think", invitation.Body);
+      Assert.EndsWith("(sent from gclo 1.2.3 (abc1234))", invitation.Body);
+   }
+
+
+
+   [Fact]
+   public void TheLink_OpensANewMessage_WithNoRecipient_AndCarriesSubjectAndBodyExactly()
+   {
+      ShareInvitation invitation = Invitation();
+      string link = invitation.MailtoUri.OriginalString;
+
+      Assert.Equal("mailto", invitation.MailtoUri.Scheme);
+      Assert.StartsWith("mailto:?subject=", link); // nothing between "mailto:" and "?": the user types the address
+      string[] parts = link["mailto:?".Length..].Split('&');
+      Assert.Equal(2, parts.Length);
+      Assert.Equal(invitation.Subject, Uri.UnescapeDataString(parts[0]["subject=".Length..]));
+      Assert.Equal(invitation.Body, Uri.UnescapeDataString(parts[1]["body=".Length..]));
+   }
+
+
+
+   [Fact]
+   public void TheLink_IsShortEnoughForMailProgramsThatCutLongOnes_AndHasNoRawSpaceOrLineBreak()
+   {
+      string link = Invitation().MailtoUri.OriginalString;
+
+      Assert.True(link.Length < ShareInvitation.MaxLinkLength, $"the link is {link.Length} characters long");
+      Assert.True(Invitation().FitsInALink);
+      Assert.DoesNotContain(' ', link);
+      Assert.DoesNotContain('\n', link);
+      Assert.DoesNotContain('\r', link);
+      Assert.Contains("%0D%0A", link, StringComparison.Ordinal); // line ends travel as CR LF
+   }
+
+
+
+   [Fact]
+   public void TheBody_IsPlainText_WithCrLfLineEnds_AndNoLineThatAMailProgramWouldMangle()
+   {
+      string body = Invitation().Body;
+
+      Assert.DoesNotContain("\n", body.Replace("\r\n", "", StringComparison.Ordinal), StringComparison.Ordinal);
+      Assert.All(body.Split("\r\n"), line => Assert.Equal(line.TrimEnd(), line));
+   }
+
+
+
+   [Fact]
+   public void AsPlainText_IsWhatAPersonCanPasteIntoAMessage()
+   {
+      ShareInvitation invitation = Invitation();
+
+      Assert.Equal("Subject: " + invitation.Subject + "\r\n\r\n" + invitation.Body, invitation.AsPlainText);
+   }
+
+
+
+   [Fact]
+   public void ATrailingSlashOnTheRepositoryAddress_DoesNotDoubleUpInTheLinks()
+   {
+      var invitation = ShareInvitation.Create(Repository + "/", " 1.2.3 ");
+
+      Assert.Contains(Repository + "/releases/latest", invitation.Body);
+      Assert.DoesNotContain("gclo//", invitation.Body);
+      Assert.EndsWith("(sent from gclo 1.2.3)", invitation.Body);
+   }
+
+
+
+   [Fact]
+   public void SpaceAroundTheAddress_IsNotPartOfTheLinks()
+   {
+      var invitation = ShareInvitation.Create("  " + Repository + "  ", "1.2.3");
+
+      Assert.Contains("\r\n" + Repository + "/releases/latest\r\n", invitation.Body);
+   }
+
+
+
+   [Fact]
+   public void AnInvitationTooLongForALink_SaysSo()
+   {
+      var invitation = ShareInvitation.Create("https://example.test/" + new string('a', 1200), "1.2.3");
+
+      Assert.True(invitation.MailtoUri.OriginalString.Length > ShareInvitation.MaxLinkLength);
+      Assert.False(invitation.FitsInALink);
+   }
+
+
+
+   [Theory]
+   [InlineData("")]
+   [InlineData("   ")]
+   [InlineData("not a web address")]
+   [InlineData("ftp://example.test/gclo")]
+   [InlineData("/relative/path")]
+   [InlineData("https://someone:secret@example.test/gclo")] // a name and a password would travel in every link
+   [InlineData("https://example.test/gclo?tab=readme")]
+   [InlineData("https://example.test/gclo#readme")]
+   public void AnAddressThatIsNotAPlainWebAddress_IsRefused(string repositoryUrl)
+       => Assert.ThrowsAny<ArgumentException>(() => ShareInvitation.Create(repositoryUrl, "1.2.3"));
+
+
+
+   [Theory]
+   [InlineData("1.2.3\r\nBcc: someone@example.test")]
+   [InlineData("1.2.3\nmore")]
+   [InlineData("1.2.3\t(x)")]
+   public void AVersionWithAControlCharacter_IsRefused(string version)
+       => Assert.ThrowsAny<ArgumentException>(() => ShareInvitation.Create(Repository, version));
+
+
+
+   [Fact]
+   public void AMissingVersion_IsRefused()
+   {
+      Assert.ThrowsAny<ArgumentException>(() => ShareInvitation.Create(Repository, " "));
+      Assert.ThrowsAny<ArgumentException>(() => ShareInvitation.Create(Repository, null!));
+      Assert.ThrowsAny<ArgumentException>(() => ShareInvitation.Create(null!, "1.2.3"));
+   }
+}
diff --git a/gclo.UiTests/SmokeTests.cs b/gclo.UiTests/SmokeTests.cs
index f29cc2b..6eff845 100644
--- a/gclo.UiTests/SmokeTests.cs
+++ b/gclo.UiTests/SmokeTests.cs
@@ -95,6 +95,33 @@ public sealed partial class SmokeTests : UiTestBase
 
 
 
+   // Help -> Share gclo by email. Under the fixture the invitation is shown in the
+   // app instead of being handed to an email program, so the test can read it and
+   // nothing opens on the machine that runs the suite.
+   [Fact]
+   public void HelpMenu_Share_ShowsTheInvitation_WithTheDownloadLink()
+   {
+      Session.InvokeMenuItem("Help", "MenuShare");
+      try
+      {
+         AutomationElement text = Session.WaitForElement("ShareInvitationText");
+         string invitation = text.Patterns.Value.Pattern.Value.Value;
+
+         Assert.StartsWith("Subject: Try gclo", invitation, StringComparison.Ordinal);
+         Assert.Contains("https://github.com/KofTwentyTwo/gclo/releases/latest", invitation, StringComparison.Ordinal);
+         Assert.False(Session.App.HasExited);
+
+         Session.ClickButton("Close");
+         Session.WaitForElementGone("ShareInvitationText");
+      }
+      finally
+      {
+         Session.TryClickButton("Close"); // no-op when the happy path closed it
+      }
+   }
+
+
+
    // (5) Help -> About shows the semantic version plus the parenthesized git hash.
    [Fact]
    public void HelpMenu_About_ShowsSemanticVersionWithCommitHash()
diff --git a/gclo.ViewModels/ShareInvitation.cs b/gclo.ViewModels/ShareInvitation.cs
new file mode 100644
index 0000000..f3fcd23
--- /dev/null
+++ b/gclo.ViewModels/ShareInvitation.cs
@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2026 James Maes (KofTwentyTwo)
+ * SPDX-License-Identifier: MIT
+ */
+
+namespace gclo.ViewModels;
+
+
+/// <summary>
+/// An invitation to try the app, written as an email that the user's own mail
+/// program opens ready to send: a subject, a plain-text body that says what the app
+/// is, where to download the latest release, and how to install it, and the
+/// <c>mailto:</c> link that carries both. The link names no recipient, so the user
+/// types an address and sends. Nothing is sent by the app, and nothing about the
+/// user, their accounts, or their repositories is in the text.
+/// </summary>
+public sealed class ShareInvitation
+{
+   /// <summary>
+   /// The longest <c>mailto:</c> link worth handing to a mail program: some of them
+   /// cut a longer one short. The text is written to stay well below this; see
+   /// <see cref="FitsInALink"/> for an invitation that does not.
+   /// </summary>
+   public const int MaxLinkLength = 2000;
+
+
+
+   private ShareInvitation(string subject, string body)
+   {
+      Subject = subject;
+      Body = body;
+      MailtoUri = new Uri("mailto:?subject=" + Uri.EscapeDataString(subject) + "&body=" + Uri.EscapeDataString(body));
+   }
+
+
+
+   /// <summary>The subject line.</summary>
+   public string Subject { get; }
+
+   /// <summary>The message, as plain text with CR LF line ends.</summary>
+   public string Body { get; }
+
+   /// <summary>The link that opens a new message with the subject and the body filled in, and no recipient.</summary>
+   public Uri MailtoUri { get; }
+
+   /// <summary>Subject and body as one text, to show and copy when no mail program takes the link.</summary>
+   public string AsPlainText => "Subject: " + Subject + "\r\n\r\n" + Body;
+
+   /// <summary>
+   /// False when <see cref="MailtoUri"/> is longer than <see cref="MaxLinkLength"/>:
+   /// a mail program might then open with half a message, so the text is better shown
+   /// for copying.
+   /// </summary>
+   public bool FitsInALink => MailtoUri.OriginalString.Length <= MaxLinkLength;
+
+
+
+   /// <summary>Writes the invitation.</summary>
+   /// <param name="repositoryUrl">
+   /// The project's public page, which the release and documentation links hang off:
+   /// an http(s) address made of a host and a path, nothing else.
+   /// </param>
+   /// <param name="version">The running app's version, named at the end so the recipient knows what the sender uses.</param>
+   /// <exception cref="ArgumentException">
+   /// <paramref name="repositoryUrl"/> is not an absolute http(s) address, or carries
+   /// a user name, a query, or a fragment; or <paramref name="version"/> holds a
+   /// control character. Either would put something into the message that the links
+   /// and lines of it are not meant to hold.
+   /// </exception>
+   public static ShareInvitation Create(string repositoryUrl, string version)
+   {
+      ArgumentException.ThrowIfNullOrWhiteSpace(repositoryUrl);
+      ArgumentException.ThrowIfNullOrWhiteSpace(version);
+      if(!Uri.TryCreate(repositoryUrl.Trim(), UriKind.Absolute, out Uri? page) || page.Scheme is not ("https" or "http"))
+      {
+         throw new ArgumentException($"'{repositoryUrl}' is not a web address.", nameof(repositoryUrl));
+      }
+      if(page.UserInfo.Length > 0 || page.Query.Length > 0 || page.Fragment.Length > 0)
+      {
+         throw new ArgumentException(
+             "The project's page is a host and a path: no user name, no query, no fragment.", nameof(repositoryUrl));
+      }
+      if(version.Any(char.IsControl))
+      {
+         throw new ArgumentException("The version is one line of text.", nameof(version));
+      }
+
+      // From the parsed address, not from the text as given: what goes into the
+      // message is the scheme, the host, and the path, and nothing more.
+      string repository = page.GetLeftPart(UriPartial.Path).TrimEnd('/');
+      string[] lines =
+      [
+          "Hi,",
+          "",
+          "I use gclo and thought you might like it. It is a small Windows app (with a command-line version) that "
+          + "clones every repository of a GitHub organization or account into a folder and keeps them up to date.",
+          "",
+          "Download the latest release:",
+          repository + "/releases/latest",
+          "Get gclo-stable-Setup.exe there. It installs for your user only (no admin rights) and updates itself.",
+          "",
+          "Command line only, with Scoop:",
+          "scoop bucket add gclo " + repository,
+          "scoop install gclo",
+          "",
+          "How to use it: " + repository + "#readme",
+          "",
+          "If you try it, tell me what you think.",
+          "",
+          "(sent from gclo " + version.Trim() + ")",
+      ];
+      return new ShareInvitation(
+          "Try gclo: clone and update every repository of a GitHub organization", string.Join("\r\n", lines));
+   }
+}
diff --git a/gclo/MainWindow.xaml b/gclo/MainWindow.xaml
index c692f7e..df6af48 100644
--- a/gclo/MainWindow.xaml
+++ b/gclo/MainWindow.xaml
@@ -33,6 +33,7 @@
                 <MenuFlyoutItem Text="View on GitHub" AccessKey="G" AutomationProperties.AutomationId="MenuGitHub" Click="GitHubMenuItem_Click" />
                 <MenuFlyoutItem Text="Submit an issue…" AccessKey="I" AutomationProperties.AutomationId="MenuSubmitIssue" ToolTipService.ToolTip="Report a bug or request a feature on GitHub" Click="SubmitIssueMenuItem_Click" />
                 <MenuFlyoutItem Text="Community support…" AccessKey="S" AutomationProperties.AutomationId="MenuCommunitySupport" ToolTipService.ToolTip="Ask a question or share tips in GitHub Discussions" Click="CommunitySupportMenuItem_Click" />
+                <MenuFlyoutItem Text="Share gclo by email…" AccessKey="E" AutomationProperties.AutomationId="MenuShare" ToolTipService.ToolTip="Draft an invitation with download links in your email program" Click="ShareMenuItem_Click" />
                 <MenuFlyoutSeparator />
                 <MenuFlyoutItem x:Name="CheckUpdatesMenuItem" Text="Check for updates…" AccessKey="C" AutomationProperties.AutomationId="MenuCheckUpdates" Click="CheckForUpdatesMenuItem_Click" />
                 <MenuFlyoutSeparator />
diff --git a/gclo/MainWindow.xaml.cs b/gclo/MainWindow.xaml.cs
index 54451ba..e5f6e77 100644
--- a/gclo/MainWindow.xaml.cs
+++ b/gclo/MainWindow.xaml.cs
@@ -1164,6 +1164,130 @@ public sealed partial class MainWindow : Window
 
 
 
+   /// <summary>
+   /// Help > Share gclo by email: hands an invitation (what gclo is, where to download
+   /// it, how to install it) to the user's email program as a
+   /// new message with no recipient, so they type an address and send. gclo sends
+   /// nothing itself. When no email program takes it, the text is shown, and copied
+   /// to the clipboard when the clipboard can be had, to be pasted into a message by
+   /// hand.
+   /// </summary>
+   private async void ShareMenuItem_Click(object sender, RoutedEventArgs e)
+   {
+      try
+      {
+         var invitation = ShareInvitation.Create(RepoUrl, BuildVersion.Describe(typeof(MainWindow).Assembly));
+
+         // The UI suite must not open an email program on the machine it runs on,
+         // nor touch the clipboard, which belongs to the whole desktop (it would
+         // overwrite what the person at the machine copied): under its fixture the
+         // invitation is only shown.
+         bool isUnderTest = UiTestFixture.IsEnabled;
+         if(!isUnderTest && invitation.FitsInALink && await TryOpenInEmailProgramAsync(invitation))
+         {
+            _log.Info("Share: the invitation was handed to the email program.");
+            return;
+         }
+
+         // When another program holds the clipboard the text is still shown, to be
+         // copied by hand; the dialog says which of the two it is.
+         bool copied = !isUnderTest && TryCopyToClipboard(invitation.AsPlainText);
+         ContentDialogResult? shown = await DialogGuard.ShowAsync(NewShareDialog(invitation, copied));
+         _log.Info(
+             (isUnderTest ? "Share: under the UI test fixture no email program is asked; " : "Share: no email program took the invitation; ")
+             + (copied ? "it was copied to the clipboard and " : "it was ")
+             + (shown is null ? "could not be shown, because another dialog is open." : "shown."));
+      }
+      catch(Exception ex)
+      {
+         // Nothing depends on this action; a failure is said in the log, not as a crash.
+         _log.Error($"Share: the invitation could not be opened ({ex.Message}).", ex);
+      }
+   }
+
+
+
+   /// <summary>
+   /// Asks Windows to open the invitation in the email program; false when none took
+   /// it, or when asking failed, which is said in the log and treated the same way.
+   /// </summary>
+   private async Task<bool> TryOpenInEmailProgramAsync(ShareInvitation invitation)
+   {
+      try
+      {
+         return await Windows.System.Launcher.LaunchUriAsync(invitation.MailtoUri);
+      }
+      catch(Exception ex)
+      {
+         _log.Error($"Share: the email program could not be asked ({ex.Message}).", ex);
+         return false;
+      }
+   }
+
+
+
+   /// <summary>Puts text on the clipboard; false, with a line in the log, when the clipboard cannot be had.</summary>
+   private bool TryCopyToClipboard(string text)
+   {
+      try
+      {
+         var package = new Windows.ApplicationModel.DataTransfer.DataPackage();
+         package.SetText(text);
+         Windows.ApplicationModel.DataTransfer.Clipboard.SetContent(package);
+         // Hand the text over for good: without this it is gone when gclo closes.
+         Windows.ApplicationModel.DataTransfer.Clipboard.Flush();
+         return true;
+      }
+      catch(Exception ex)
+      {
+         // Another program holds the clipboard: not worth failing the action for.
+         _log.Error($"Share: the invitation could not be copied to the clipboard ({ex.Message}).", ex);
+         return false;
+      }
+   }
+
+
+
+   /// <summary>The invitation as text to paste, for when no email program opened it.</summary>
+   /// <param name="invitation">The invitation to show.</param>
+   /// <param name="copied">True when the text is on the clipboard already; the dialog says which it is.</param>
+   private ContentDialog NewShareDialog(ShareInvitation invitation, bool copied)
+   {
+      // AcceptsReturn before Text: a box that takes one line keeps only the first
+      // line of what it is given, which here would be the subject and nothing else.
+      var text = new TextBox
+      {
+         AcceptsReturn = true,
+         TextWrapping = TextWrapping.Wrap,
+         IsReadOnly = true,
+         MaxHeight = 320,
+         Text = invitation.AsPlainText,
+      };
+      string explanation = copied
+          ? "No email program opened the invitation. It has been copied to the clipboard: paste it into a new message, add an address, and send."
+          : "No email program opened the invitation. Copy the text below into a new message, add an address, and send.";
+      Microsoft.UI.Xaml.Automation.AutomationProperties.SetAutomationId(text, "ShareInvitationText");
+      Microsoft.UI.Xaml.Automation.AutomationProperties.SetName(text, "Invitation text");
+      // Focus lands in the box: a screen reader then also says why the dialog is there.
+      Microsoft.UI.Xaml.Automation.AutomationProperties.SetHelpText(text, explanation);
+      ScrollViewer.SetVerticalScrollBarVisibility(text, ScrollBarVisibility.Auto);
+
+      var panel = new StackPanel { Spacing = 12 };
+      panel.Children.Add(new TextBlock { Text = explanation, TextWrapping = TextWrapping.Wrap });
+      panel.Children.Add(text);
+
+      return new ContentDialog
+      {
+         Title = "Share gclo by email",
+         Content = panel,
+         CloseButtonText = "Close",
+         DefaultButton = ContentDialogButton.Close,
+         XamlRoot = Content.XamlRoot,
+      };
+   }
+
+
+
    /// <summary>Opens a page of the repository in the default browser; the log names the page, never a token.</summary>
    private async Task OpenRepositoryPageAsync(string path)
    {