IMAP, POP & SMTP Client Access
Understanding the Concept
Exchange Online supports IMAP, POP3, and SMTP protocols for legacy client compatibility. IMAP provides server-side email access, POP3 downloads messages to the client, and SMTP AUTH handles authenticated email submission.
These protocols can be enabled or disabled at the organization level and per mailbox. Due to security concerns, Microsoft recommends disabling legacy protocols and using modern authentication with Outlook or Graph API.
SMTP AUTH is commonly used for devices and applications that need to send email (printers, scanners, LOB applications). It requires careful management as it's a common attack vector for compromised accounts.
Key Points
Why This Matters
While modern clients use MAPI/HTTP, many line-of-business applications, devices, and third-party tools still require IMAP, POP, or SMTP access. Properly managing these protocols balances compatibility with security.