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.