550 No such local user processed as Soft Bounce

[Alpha1]

Affected version

2.3.10

These bounce messages should be hard bounces:

• 550 No such local user, unauthenticated relaying denied
• 550 Invalid Recipient

Same issue as this one, but with slightly different text:

Fixed Thread '550 permanent failure processed as Soft Bounce'

Nov 7, 2025

This bounce message is incorrectly processed as a Soft Bounce:

Action: failed
Final-Recipient: rfc822; xxx@evansinc.com
Diagnostic-Code: smtp; 550 permanent failure for one or more recipients (xxx@evansinc.com:550 5.4.1 Recipient address rejected: Access denied. For more information see https://aka.ms/EX...)
Status: 5.3.0

This clearly should be treated as a hard bounce.

• Alpha1
• bounce handling
• Replies: 4
• Forum: Resolved bug reports

 

[Alpha1]

Some more:

• smtp; 550 5.4.1 Recipient address rejected: Access denied
• smtp;550 5.1.10 RESOLVER.ADR.RecipientNotFound

The first one is a frequently occurring one by Microsoft.

 

[Alpha1]

• smtp; 5.1.0 - Unknown address error 550-'5.4.1 Recipient address rejected: Access denied.

Not a 550, but the same principle: as the recipient is not found

• "smtp; 554 5.7.1 recipient 'xxx@domain.com' not known

 

[smallwheels]

Another one that is currently processed as soft bounce but should potentially be a hard bounce as it is a permanent failure:

Action: failed
Status: 5.0.0
Remote-MTA: dns; mta7.am0.yahoodns.net
Diagnostic-Code: smtp; 554 Message permanently deferred due to unresolvableRFC.5321 from domain. See https://senders.yahooinc.com/error-codes#unresolvable-from-domain

Said URL says:

Unresolvable RFC.5321 or RFC.5322 from domain

• These errors indicate that the domain used to the right of the @ in the MAIL FROM or HEADER FROM does not appear to be valid.
• We determine if the domain name exists by using an SOA query; therefore, if multiple subdomains are used in MAIL FROM or HEADER FROM commands, then besides setting up a DNS A or MX record (perhaps using a wildcard), then SOA records must be set up as well.
• These errors can be returned as either a timeout/servfail (451) or a permfail (554)

(See also here: https://xenforo.com/community/threads/strange-error-554-with-mail-sent-to-yahoo.236555/ )

 

[Alpha1]

The SMTP status codes in this bug report relate to the recipient not being available. Therefore the accounts of the forum members should be set to bounced status.

The smtp status code unresolvableRFC.5321 means that there is an issue with the sender. (or at least yahoo thinks so) It is not related to the forum member, and should not have an effect on bounce status.
Its an error and a case can be made that it therefore should be in the error log.

 

[smallwheels]

The smtp status code unresolvableRFC.5321 means that there is an issue with the sender. (or at least yahoo thinks so)

That is true. The weird thing is that in this case the mail bounced was the notification mail for the welcome PN in the forum after registration. Minutes before that the registration confirmation mail was sent to the same mail-address w/o issues. Also, we do have a bunch of members with yahoo addresses an never had this failure. So basically it is a "yahoo don't know what they are doing" thing.

It is not related to the forum member, and should not have an effect on bounce status.

True and maybe not. They say it would be a permanent error. I am not willing to jump through loops just b/c yahoo decides to go berserk for no reason. If the mail provider of a user bounces a mail for no reason I ask the user to change his mail address as this is out of my influence.

It's an error and a case can be made that it therefore should be in the error log.

True as well and it was not.

As I said: It is in my eyes a bit of a grey area wether this should be considered a hard bounce or a soft bounce.