Yahoo SMTP 8 BITMIME bug

It’s sometimes hard to believe, that even the biggest make such mistakes.

Here’s the capability (EHLO) response from Yahoo’s SMTP server:

S: 220 smtp.mail.yahoo.com ESMTP ready
C: EHLO [192.168.0.11]
S: 250-smtp.mail.yahoo.com
S: 250-PIPELINING
S: 250-SIZE 41697280
S: 250-8 BITMIME
S: 250 STARTTLS

Can you spot the problem? It’s not that easy, and it has been brought to my attention by one of our customers:

S: 220 smtp.mail.yahoo.com ESMTP ready
C: EHLO [192.168.0.11]
S: 250-smtp.mail.yahoo.com
S: 250-PIPELINING
S: 250-SIZE 41697280
S: 250-8 BITMIME
S: 250 STARTTLS

It supposed to be: 8BITMIME, at least according to RFC6152

the EHLO keyword value associated with the extension is 8BITMIME;

Most annoying part is that in many cases, space is used to split extensions keyword and its parameters e.g. SIZE 41697280. We want Mail.dll to be robust enough to accept custom extensions or extensions unknown yet, that follow this standard.

Shame on you Yahoo!.

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