VBA MailToProxy - the CreateEmail procedure

This module contains the CreateEmail procedure which allow you to create an email in the default mail client in edit mode using MailTo. It provides fallbacks to Gmail/Outlook.com.

• The created email is simple, it only supports plain text.
• There is no way to actually send the mail without the user being involved.
• CC and BCC field implementation have been commented out but you can easily reintroduce them if needed.
• No error handling, any errors occurring will trickle to the calling procedure and should be handled there. Calling the procedure is simple:

CreateEmail "john@doe.com", "about MailTo",  "This is only for no frills emails"

Troubleshooting

The CreateEmail procedure relies on ShellExecute to launch the default mail client using a mailto: URL. If the email window does not appear, one of the following issues is likely the cause:

No default mail client is configured

Windows must have an application associated with the mailto: protocol.
If none is set, ShellExecute returns error 31 (SE_ERR_NOASSOC) and nothing opens.

Mail client is installed but not properly registered

Some email programs fail to register the mailto: handler correctly.
Symptoms include:

• No email window appearing
• Error 31
• The wrong application opening

URL too long or contains invalid characters

mailto: URLs have practical length limits. Unencoded characters (spaces, %, &, line breaks) or very long bodies may cause:

• Silent failure
• Truncated fields
• Generic errors such as 2 (SE_ERR_FNF) or 5 (SE_ERR_ACCESSDENIED)

Mail client rejects or mishandles the request

Certain clients—especially Outlook desktop—may:

• Ignore parameters
• Fail to open if another instance is busy
• Open a blank message instead of the expected content

Corporate or system policy restrictions

In managed environments, protocol handlers like mailto: may be disabled.
This typically results in SE_ERR_ACCESSDENIED (5) or no visible action.

Webmail handlers misconfigured

If the user has set Gmail or Outlook.com as the default handler via a browser:

• The browser may fail to launch
• Parameters may not be passed correctly
• The wrong profile may open

The built‑in fallback to Gmail/Outlook.com helps mitigate this scenario.

How to Fix

If CreateEmail fails to open a new message window, try the following steps:

1. Verify the default mail client

Check Settings → Apps → Default apps → Choose defaults by link type → mailto
Ensure a valid desktop mail client (Outlook, Thunderbird, etc.) is selected.

2. Test the mailto handler directly

Open Run (Win+R) and enter:

mailto:test@example.com

If nothing happens, the system’s mailto: association is broken.

3. Shorten or encode the email body

Long bodies or unencoded characters can break the URL.
Try:

• Reducing the body length
• Ensuring proper URL encoding (spaces → %20, line breaks → %0D%0A)

4. Restart or repair the mail client

Some clients (especially Outlook) may need:

• A restart
• A profile repair
• A system reboot

5. Check corporate or system restrictions

On managed devices, protocol handlers may be disabled.
Contact IT if:

• mailto: does nothing
• You receive Access Denied errors

6. Try the built‑in webmail fallback

If the desktop handler fails, the procedure automatically falls back to:

• Gmail
• Outlook.com

This ensures the user can still compose an email even when the local handler is misconfigured.

---