Over the last few months I’ve seen people complaining about losing the Yahoo FBL emails with verification codes. This seems to be intermittent and no one could really explain what was going on.
Dale Lopez, VP of operations for V12 group, shared that their operations group discovered that one issue with the missing verification emails has to do with the length of the From: address and a port25 default settings.
In Dale’s words:
We figured it out and have confirmed via test. . . If you are a PowerMTA user (Port25 Solutions), the default from line that PMTA accepts is set to 64. The from line that Yahoo has in the verification code message, is much longer. If you increase the length of the maximum characters to 254, you should receive the verification email.
So if you’re having problems receiving the Yahoo verification emails, check with your IT department to make sure you’re not restricting the path length. The “path” in this case is the return-path address. RFC 5321 says “the maximum total length of a reverse-path or forward-path is 256 octets (including the punctuation and element separators).” Reverse-Path in this case is the address in the envelope from, Forward-Path is the address in the To: line.
So if you’re one of the companies having problems receiving the Y! verification email, check you incoming mail settings and make sure you’re not blocking long email addresses.
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Ooh, good catch.
Wonderful! Do you know what the PMTA directive is to fix this?
This is what you need
max-address-local-part-length 128
To clarify, this is a Yahoo bug, *not* a PowerMTA bug – RFC 5321 is very clear that the local parts of email addresses MUST NOT be longer than 64 bytes, and Yahoo is violating that.
PowerMTA is – quite correctly – rejecting those messages because, well, they’re not email. Violating SMTP standards is something spammers do, so you’re _usually_ going to be happy when your mailserver enforces them.
I completely agree with Steve – lucky Port25 has the directive I posted above that allows for this. You simply put it in your Source 0/0.
I find it strange that yahoo would dump return path’s management of their FBL in lieu of a non compliant solution. (Not that I’m anamored with RP) but you’d think that yahoo would be setting examples, not breaking RFC
Laura and Dale, thanks for sharing this. Our V12 Group team was stumped for a over a week. Thanks to our network ops team and their sniffer, we were able to intercept part of the communication coming from Yahoo and concluded that they were exceeding the address-local-part.
Great to share it.
We actually discovered it 1.5 months ago and then Port25 shared this undocumented directive with Postmastery.
It should be added to the :
<source 0/0
max-address-local-part-length 128
Make sure you have at-least PMTA v4.0r19.