Gmail’s intermediate SSL certificate for the Simple Mail Transfer Protocol (SMTP) appears to have expired, causing issues for new users trying to send email via Gmail or Google Apps with the standard.

Update: Google acknowledged that “smtp.gmail.com is displaying an invalid certificate” on its Apps Status Dashboard today. By 12:46 p.m. Pacific — more than an hour after this post was published — Google said that “the problem with Gmail should be resolved.”

The expired certificate for the smtp.google.com domain was spotted earlier today by Twitter user 925dk. A couple of VentureBeat writers verified the problem by attempting to add a Gmail account to various email clients.

Here’s the SMTP error you received when trying to add a Gmail account in OS X’s Mail:

Trying to use my personal Gmail on Mail on a Mac.

Above: Trying to use my personal Gmail on Mail on a Mac.

Image Credit: Screen shot

Google Internet Authority G2 issues digital certificates for Google domains, though currently only the smtp.gmail.com appears to be affected. A more generic error showed up in Outlook for Windows:

gmail_smtp_fail

The good news is that the error did not appear to affect all email accounts that had already been added to email clients. (One person did write in to tell us this happened, although we weren’t able to reproduce it.) As such, most Gmail users can continue to send email over SMTP. If you’d tried to add your account today, however, you would have run into problems when using SMTP.

Updated at 1:31 p.m. Pacific to reflect that the problem appears to be solved now.