Currently, if we need to use EMail Logger Sink in Serilog, we have to use it with NetworkCredentials (Basic Auth) i.e., UserName / Password combo. Now, as per below link from Microsoft, Exchange Online is deprecating and stopping usage (not just support, but they are completely stopping usage) of Basic Auth for SMTP from March 2026

https://techcommunity.microsoft.com/blog/exchange/exchange-online-to-retire-basic-auth-for-client-submission-smtp-auth/4114750

Thereby, for projects who use Serilog with Email Logger Sink and use Microsoft Exchange Online for SMTP mailing, there is no possible way to use SeriLog Email Logger Sink going forward. Thereby, support needs to be provided from SeriLog to make use of SMTP OAuth or Graph API so that Microsoft Exchange Mail clients can still continue using SeriLog