What version of outlook?

Hello! We'd be happy to take a look at this for you as well. First; I have a couple of questions to help us get some more details: 

- Have you identified any common variables across the users who can't use Reply All functionality? 

- Are all of the affected users on the same version of Outlook and using the MAPI protocol? 

- Are there specific threads that this happens on more often than not?

- What version of SmarterMail is in use here?

Different outlook version 2019/2021/2024, the acoount afflicted MAPI.

Different customer, different domain, different firewall, different email, the only common is Smartermail server

Latest version of SM

Are you or one of these users able to replicate on demand, or is this more sporadic? I ask because a Fiddler trace may be best in getting an idea of what it is doing since the issue looks to be happening inside of Outlook somewhere. Can I have you download and install Fiddler Web Debugger (Classic), configure to decrypt HTTPS traffic, then run it while reproducing the issue a couple of times? At that point you can export it as an SAZ file and send that our way in a ticket for review. Thank you in advance. 

This is the email fo my customer:

"non è visibile il mittente e anche quando faccio un inoltra, nella mail che inoltro non si vede il mittente, ti allego screenshot.

È un’impostazione assolutamente da sistemare.

La questione del “rispondi a tutti” infine è per noi molto importante poiché mandiamo mail anche a 10 destinatari e, dato che sono più settimane che riscontriamo questo errore, urge una rapida soluzione"

news for the new release of the software that solve the problem?

I have installed windows 11 and office english version in a laptop i have the same problem, reply all not working and sender missing, i don't understand how you are unable to replicate the problem.