SMTPUTF8

Question asked by Sébastien Riccio - 2/29/2024 at 1:17 PM

Unanswered

Hello,

While trying to troubleshoot recent outgoing mail (SMTP) issues for a customer using Outlook, I noticed in the SMTP log in that his mails are rejected by SmarterMail because of:

555 Unsupported parameter: SMTPUTF8

It seems that Outlook doesn't care if SMTPUTF8 support is announced or not in capabilities returned by the server and try to use the parameter anyway.

After being authenticated, Outlook sends:

MAIL FROM: <some@mailaddress.tld> SMTPUTF8

And as SMTPUTF8 is not supported by SmarterMail, it is rejected.

Now I don't understand why Outlook would use SMTPUTF8 here, as far as I know, it is only needed if you use international chars in e-mail addresses, and this is very rare imho.

Still, I've searched the SMTP logs on our SmarterMail install for "555 Unsupported parameter: SMTPUTF8" and there are a huge amounts of matches.

Are you also seeing a lot of these in your systems ?

Kind regards

Sébastien Riccio

System & Network Admin

https://swisscenter.com

13 Replies

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Brian Replied

2/29/2024 at 2:28 PM

No results here when searching SMTP logs.

Sébastien Riccio Replied

2/29/2024 at 2:37 PM

Ok thank you. Very strange then...

Sébastien Riccio

System & Network Admin

https://swisscenter.com

echoDreamz Replied

2/29/2024 at 3:17 PM

Same, nothing

SMTPUTF8

Related in our logs either.

Gabriele Maoret - SERSIS Replied

2/29/2024 at 4:27 PM

No results here too when searching "SMTPUTF8" in SMTP logs....

Gabriele Maoret - Head of SysAdmins and CISO at SERSIS

Currently manages 7 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 6 on-premise for customers who prefer to have their mail server in-house)

Sébastien Riccio Replied

2/29/2024 at 4:34 PM

Ok thanks for the feedbacks. Are your SMTP logs set to detailed ? I think they pop only in detailed mode.

If they are then I'll have to dig deeper at our side to understand what's going on.

Sébastien Riccio

System & Network Admin

https://swisscenter.com

Gabriele Maoret - SERSIS Replied

2/29/2024 at 4:37 PM

Yes, my SMTP log is set to "detailed"...

Gabriele Maoret - Head of SysAdmins and CISO at SERSIS

echoDreamz Replied

2/29/2024 at 4:49 PM

Same, SMTP logs are "Detailed".

Kyle Kerst Replied

2/29/2024 at 4:53 PM

Employee Post

I wasn't able to find any references to this error across the various test servers we sync to either.

Kyle Kerst

Lead Internal Network/System Administrator

SmarterTools Inc.

smartertools.com

Sébastien Riccio Replied

2/29/2024 at 5:03 PM

Thank you again for the feedbacks. I'll investigate this more deeply at our side then.

Kind regards

Sébastien Riccio

System & Network Admin

https://swisscenter.com

J. LaDow Replied

2/29/2024 at 9:41 PM

Our logs are set to detailed, we went back 15 days and have not seen that in our report - we are not on the latest version though -- still running build 8657 -- not sure if that helps when tracking this issue.

MailEnable survivor / convert --

Sébastien Riccio Replied

2/29/2024 at 10:47 PM

Thank you all.

After checking all our SMTP logs containing a huge amount of these entries, they seems to be linked to only a few users but repeated multiple times per hour.

I hope it's not users that have their Outlook updated to the latest version that triggers this issue...

I keep on digging...

Sébastien Riccio

System & Network Admin

https://swisscenter.com

Sébastien Riccio Replied

3/1/2024 at 12:30 AM

Well I found the issue while working on it with one of our affected customer.

These customers mistakenly tried to send a mail to a mail address CONTAINING an accented character, and this trigger the need of SMTPUTF8 (not supported by SM).

The mail is then stuck in the Outlook outbox and it keeps on retrying sending it over and over again.

But then there is a side effect to this. When the customer tries to delete the mail from the Outbox, Outlook will want to move it to Deleted items, and this brings another problem as Outlook then tries to sync the Deleted item with the server (through IMAP) and this is also rejected by SM.

I was able to reproduce all this with a test mailbox and Outlook with IMAP/SMTP and a mail that has at least on recipient having an accent in the address.

The outlook syncher returns this when tried to sync the deleted item (sorry for french log):

08:28:52 Synchronisateur Version 16.0.17328.20108
08:28:52 Synchronisation de la boîte à lettres 'madjik@cybermind.ch' en cours
08:28:52 Synchronisation des modifications locales dans le dossier « Deleted Items » en cours
08:28:52 Erreur lors de la synchronisation du message 'test stufff'
08:28:52 		 [800CCE46-0-0-322]
08:28:52 Terminé

So well, it seems the situation can be resolved by using shift-delete instead of delete when deleting the stuck mail, but that's still an interresting issue...

To summarize:

1) SMTPUTF8 is pure useless crap (as are IDN domain names)

2) But still, it is supported by quite some clients and mail services so SM might want to consider supporting it too. However because of 1) i understand it's not a top priority...

3) Outlook should not attempt to send the mail when it requires SMTPUTF8 but the feature is not advertised by the SMTP server.

Kind regards

Sébastien Riccio

System & Network Admin

https://swisscenter.com

Igor Varfolomeev Replied

3/8/2025 at 9:59 PM

Just in case anyone would run into this....

I just ran into [800CCE46-0-0-322] as well. This seem to be related to UTF-8 characters in email address. On the first glance, the email address looked perfectly normal, but there actually was a special character in there (only noticeable using a hex editor).

Many email servers do not support UTF8 email addresses, including gmail.com , for example (which is a good idea, because with UTF-8 you can create non-equal but very similar-looking strings, which would allow dangerous scam/spam). But some servers (e.g. Microsoft Exchange) perfectly work with them.

The fact that this error code seem to be undocumented is frustrating. I've just filed an improvement suggestion here: https_:_ // feedbackportal.microsoft.com/feedback/idea/3b01c8d0-9bfc-ef11-a4dd-7c1e52ead3c1 (sorry, I'm not allowed to post the links here, but I've registered here just to post this).

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