Outlook 2019: search on server not working

[RiccardoDellaPace]

Hi everyone,

we have a problem, maybe caused by an Antivirus, that I can't manage to solve.
The local Client of Outlook could't perform research "on server".

Does anyone know how does this search work?
URL, Port, protocol?

Thanks in advance

[#2]

Hi @RiccardoDellaPace 

Can you clarify if the user's mailbox is on Exchange On-Prem or Office 365? What is showing when the user tries to search?

[#3]

Office 365 in this case

[#4]

@RiccardoDellaPace check the following article: https://support.office.com/en-us/article/troubleshooting-outlook-search-issues-2556b11f-f4d8-46be-b0... 

If you disable the AV, is Outlook search working correctly? 

[#5]

@George Marian Neagoe yes, disabling the AV it works; that's why I'm looking for urls and connections and not for Outlook's errors. 
The problem is only related to "on Server" search with AV on, local search works.

[#6]

@RiccardoDellaPace for Office 365 IPs and URLs you can check the following article:

(Exhange Online) https://docs.microsoft.com/en-us/office365/enterprise/urls-and-ip-address-ranges