SMTP server returning errors for long mailing list reply addresses

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6 posts Page 1 of 1
by tbessie » Sat Mar 05, 2022 12:09 pm
Can Sonic tech support chime in on this issue I'm having?

I'm trying to reply to a return address on a mailing list I'm on, but Sonic's SMTP server keeps thinking it's a malformed address, even though it's legal.

I've seen discussions online that this can be a configuration option or fixed by a server patch.

Any idea why your SMTP server doesn't like this address? I've masked part of it for privacy:
SMTP Error (501): Failed to add recipient "reply+BIGLONGSTRINGHERE@mg1.substack.com" (5.0.1 reply+BIGLONGSTRINGHERE@mg1.substack.com is not a valid fully qualified email addresss [cerb:INVRCPT]).
by gkeller » Mon Mar 07, 2022 3:58 pm
Hello,

From the logs I was able to find the address in question, and the local part (to the left of the @) is longer than 64 characters. That limit is supposed to be part of the engineering standards, so I couldn't tell you why the reply addresses from substack are allowed to be longer than that. I would contact substack about the issue, as I am sure we are not the only mail providers that would consider that to be an invalid email address.
Grant Keller
Sonic.net System Operations
by tbessie » Mon Mar 07, 2022 4:38 pm
Thanks for checking this out! I was hoping you would change your configuration to allow for longer email addresses, since you're more responsive to things than Substack is likely to be. But I'll look into it and see what they say. :-)

- Tim
by tbessie » Mon Mar 07, 2022 4:57 pm
I also just found out that I don't have to use the "Reply To" value, as the blog owner uses a real "To" address I can email to, so I just used that. Silly me, I hadn't noticed until just now!

Still, I wrote to Substack support and asked them if this illegal "Reply To" address is intentional.

- Tim
by kgc » Thu Mar 17, 2022 12:16 pm
FYI, we no longer are enforcing the RFC compliant 64 char 'local address part' limit on our outbound mail servers. It's an arbitrary limit and does not appear to be widely enforced and is somewhat commonly exceeded by VERP and other return path encoding schemes.
Kelsey Cummings
System Architect, Sonic.net, Inc.
by tbessie » Thu Mar 17, 2022 12:35 pm
kgc wrote:FYI, we no longer are enforcing the RFC compliant 64 char 'local address part' limit on our outbound mail servers. It's an arbitrary limit and does not appear to be widely enforced and is somewhat commonly exceeded by VERP and other return path encoding schemes.
Thanks Kelsey! I contacted Substack, and they didn't seem to care, and told me to use the other address in the emailings from them (a FROM address and not the Reply-To address). I told them to let their techs no that they were out of compliance with the RFC, and they said they'd let them know. Probably won't make a difference.

Anyway, thanks again for changing this - I learned something! :-)

- Tim
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