Microsoft will impose a throttling limit for external recipients for tenants that use MOERA domain addresses to send outbound email. The limit is designed to stop tenants using mailboxes with primary SMTP addresses from MOERA domains from sending email, a technique that’s often used by spammers. This shouldn’t cause a problem for legitimate organizations who already have vanity domains, but it might stop some spam.
Microsoft 365 makes it easy to remove domains. However, if you remove a domain and don’t adjust email proxy addresses, some fix-up might be needed to make sure that mail-enabled objects don’t have primary SMTP addresses or proxy addresses that use the removed domains. This article explains how to fix up mail-enabled objects with PowerShell to remove traces of any removed domains.
Like any mail-enabled object managed by Exchange Online, distribution list proxy addresses determine if Exchange can deliver messages to an object. Sometimes the proxy addresses aren’t correct or need adjustment, such as in the case when an organization wants to make sure that all distribution lists have primary SMTP addresses from a specific domain. This article explains how to use PowerShell to adjust the primary SMTP address when necessary.