Hi all,

I have a weird problem that started just today. I am using Apple Mail on a Leopard machine, connecting to Gmail. Fetching e-mail works just fine. My SMTP settings are also correct. Still, I can't send mail, it will display a pop up saying that "transferring the content to the mail server" failed (translation from German, could be different in English OS X versions).

I have verified the following:

• My SMTP settings are definitely correct. I have not changed them and the issue appeared today.
• Also, I went through the Apple online configuration for Gmail accounts and did not have to adjust any setting.
• I can run network diagnosis and it will connect to both POP and SMTP servers without a problem (all green lights)
• The Telnet details will show me the HELO message from the Gmail servers, so there's no authentication failure.
• Console.app will not show any messages related to "mail" when I try to send the mail, so there's no specific error message
• The mail I'm trying to send does not have an attachment, it is plaintext only
• I can login to gmail.com and send mails without a problem
• The recipient address exists and contains no syntax errors
• I can also not send mails to myself
• When using another IP and ISP (through VPN), it still doesn't work

As for my settings: I connect to smtp.gmail.com and for advanced settings I choose password-based authentication with user: [email protected] and my password. I let Apple Mail try the default ports (for SSL and TLS, respectively).

Again: I have not changed a thing between yesterday and today.

What is causing that strange behavior? Any help would be much appreciated.