Use an on-premises email server (Exchange Server or almost every other SMTP server) to relay mail Should your system is struggling to meet up with the prior needs for connecting to Microsoft 365 or Office 365. I normally propose utilizing up at least these guidelines from the security guideline: #2: https://azure-support99888.slypage.com/26596852/5-tips-about-postal-smtp-setup-you-can-use-today