Funciona bem para mim, então eu suspeito que havia um caractere extra na linha MAIL FROM confundindo o parser.
$ telnet alt3.gmail-smtp-in.l.google.com 25
Trying 173.194.66.26...
Connected to alt3.gmail-smtp-in.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP eu4si26638696wjd.51 - gsmtp
ehlo
250-mx.google.com at your service, [128.XXX.YYY.ZZZ]
250-SIZE 35882577
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250 CHUNKING
MAIL FROM:<[email protected]>
250 2.1.0 OK eu4si26638696wjd.51 - gsmtp
RSET
250 2.1.5 Flushed eu4si26638696wjd.51 - gsmtp
QUIT
221 2.0.0 closing connection eu4si26638696wjd.51 - gsmtp
Connection closed by foreign host.