Voicemail flow not sending email notification — SMTP config correct

Architect & Flows
1

Voicemail email notifications stopped working after we migrated from on-prem Exchange to Microsoft 365.

We updated the SMTP settings in GC Admin to point to the M365 SMTP endpoint (smtp.office365.com:587). Authentication succeeds, but notifications never arrive. No bounce messages, no errors in the admin panel - just silence.

2

Microsoft 365 deprecated Basic Authentication for SMTP in September 2024.

GC’s SMTP configuration only supports username/password (Basic Auth). M365 now requires OAuth2 for authenticated SMTP relay. You have two options:

  1. Configure an M365 SMTP relay connector that allows Basic Auth from GC’s IP range (less secure but functional)
  2. Use a third-party SMTP relay (Amazon SES, SendGrid, Mailgun) as an intermediary between GC and M365

Option 2 is more reliable and avoids Microsoft’s deprecation roadmap entirely.

3

We deployed Amazon SES as our SMTP relay and it solved the problem permanently.

# GC Admin SMTP Configuration
# Host: email-smtp.us-east-1.amazonaws.com
# Port: 587
# TLS: Required
# Username: <SES SMTP IAM credential>
# Password: <SES SMTP IAM credential>

# SES then forwards to M365 via verified domain
# SES handles OAuth2 complexity with Microsoft on your behalf

SES costs $0.10 per 1,000 emails. At 500 voicemails/day, that’s $1.50/month. The engineering time saved from not fighting M365 OAuth is worth 100x that.

4

Under SOC2 and PCI-DSS, voicemail notification emails that contain transcription snippets are transmitting customer PII.

Ensure your SMTP relay enforces TLS 1.2 minimum for all connections. SES enforces TLS by default, which satisfies the encryption-in-transit requirement. Also verify that the voicemail transcription doesn’t include credit card numbers or SSNs - configure the transcription engine to redact sensitive patterns before generating the email body.