I appear to be having a problem very similar to the one described in a previous thread in which the resolution was never documented.

I'm running Ubuntu 12.04 LTS. Postfix is successfully receiving inbound messages sent from every email service imaginable, except for GMail that has sent from an email client through Google's SMTP server (as opposed to GMail web mail, which is delivered fine).

I have not (yet) received the rejection email from GMail.

This is what gets written to mail.log when GMail tries to deliver the email:

May 17 10:23:29 myhostname postfix/smtpd[3547]: connect from mail-pb0-f51.google.com[209.85.160.51]
May 17 10:23:29 myhostname postfix/smtpd[3547]: warning: TLS library problem: 3547:error:140943FC:SSL routines:SSL3_READ_BYTES:sslv3 alert bad record mac:s3_pkt.c:1247:SSL alert number 20:
May 17 10:23:29 myhostname postfix/smtpd[3547]: lost connection after EHLO from mail-pb0-f51.google.com[209.85.160.51]
May 17 10:23:29 myhostname postfix/smtpd[3547]: disconnect from mail-pb0-f51.google.com[209.85.160.51]

(Nothing is written to mail.err)

I have researched this problem extensively but so far have come up empty. Any guidance would be appreciated.

Fetching mail via mail polling in gmail (e.g. by fetchmail) always requires ssl. Does that work?

Do you use any m$ based vaildation service? There was some stupid stuff in the early days when m$ hotmail refused google's mail, but the little boys were told to behave themselves.

Whatever you're using for ssl, have you tried ldd on it to see that all the libs are present & correct?

Sorry, I think we're talking about two different things. I operate an email server, and am referring to what happens when someone sends one of my users email from a GMail account.

Try adding this to the general section of main.cf

Then reload Postfix.