Microsoft 365 outbound email setup

Outlook and Exchange Online: Graph, SMTP, throttling, and security defaults for outreach mailboxes.

Graph vs SMTP

Microsoft Graph is the modern path for mailbox access with granular permissions. SMTP AUTH may be disabled tenant-wide, so verify with admin before relying on legacy SMTP for sequences.

Throttling and recipient limits

Exchange Online applies hourly and daily limits per mailbox. Burst sending from sequences can hit throttling; stagger enrollments and respect deferrals instead of retrying aggressively.

Security defaults and MFA

Conditional access and MFA affect app connections. Use dedicated outreach mailboxes with documented credential rotation rather than sharing primary executive inboxes.

Bounce and NDR handling

NDR messages should feed your suppression process. Hard failures on invalid recipients must remove contacts from active sequences immediately.

M365 checklist

• SMTP AUTH or Graph connection verified.
• SPF/DKIM/DMARC published for sending domain.
• Mailbox display name matches brand.
• Throttling observed during test ramp, not first production day.