Office 365 “Send Mail As” Issues with Proofpoint and Gmail

September 13, 2025

Office 365 accounts protected by Proofpoint via GoDaddy fail Gmail SMTP authentication, even with MFA, app passwords, and SMTP enabled everywhere.

Email Deliverability
Email Deliverability
•
1
min read
Office 365 “Send Mail As” Issues with Proofpoint and Gmail

Experiencing difficulties with connecting an Office 365 address, which has the Proofpoint solution enabled via GoDaddy, to Gmail using the 'Send mail as' feature. Neither mx1-us1.ppe-hosted.com nor the regular Microsoft SMTPs such as smtp.office365.com or smtp-mail.outlook.com are working. SMTP is enabled everywhere - GoDaddy, Office 365 Admin, Proofpoint, and MFA is disabled. Enabling MFA and generating an app password didn't help either.

Is anyone aware of a potential solution? Should I enable conditional access in Entra (this was one of the suggestions I found on Google)...? Any suggestions would be appreciated as I've spent 6+ hours trying to solve the issue.

Email Deliverability
Email Security
Office 365
Related posts
All posts
Why a 24-Email Batch Triggered a Gmail Lockout

Why a Google Drive link in a Follow Up Boss batch email triggered spam flags and a Gmail sending limit error and how proper domain authentication fixes it

Why a 24-Email Batch Triggered a Gmail Lockout
Email Deliverability
Google Postmaster v2 API Signals Upcoming v1 Deprecation

Google has updated its Postmaster v2 API documentation, signaling that the v1 API is likely approaching deprecation.

Google Postmaster v2 API Signals Upcoming v1 Deprecation
Email Deliverability
Why Email Has So Many Rules (And Why That’s a Good Thing)

Email has more rules than ever, and for good reason. Different inbox providers enforce strict standards to protect users and control spam.

Why Email Has So Many Rules (And Why That’s a Good Thing)
Email Deliverability