Google SMTP not working on Data but is working on WIFI

I am using the latest K-9 mail on Android 11 ( Moto G Stylus ). The SMTP credentials for Google are properly entered and validate. When I am using cellular data ( t-mobile ) to send an email - the send fails with “Failed to send some messages…”. When I connect through WIFI, the message gets sent as expected.

Problem is that I want to use it mostly when away from home on cellular data.

@budingraham Welcome to the forum.

T-Mobile uses its own set of (crappy) DNS resolvers… They tend to time out on some MX routes. Try activating secure DNS on your Android device. Alternatively, you could force use of open DNS resolvers such as 8.8.4.4 and 8.8.8.8 (that’s Google) or 9.9.9.9 (Quad9).