Mattermost + SendGrid = What am I doing Wrong?

After what feels like decades trying to get postfix to work on Mattermost install, I’ve given up and decided to try SendGrid as an SMTP email provider.

When I set the connection security to STARTLS I get the following error:

“Connection unsuccessful: Connection unsuccessful: failed to close connection to the SMTP server: 550 The from address does not match a verified Sender Identity. Mail cannot be sent until this error is resolved. Visit https://sendgrid.com/docs/for-developers/sending-email/sender-identity/ to see the Sender Identity requirements”

The following is in the log:

{"level":"error","ts":1624058759.579852,"caller":"mlog/log.go:251","msg":"Connection unsuccessful: failed to close connection to the SMTP server: 550 The from address does not match a verified Sender Identity. Mail cannot be sent until this error is resolved. Visit https://sendgrid.com/docs/for-developers/sending-email/sender-identity/ to see the Sender Identity requirements","path":"/api/v4/email/test","request_id":"43iipsg9tjrzdx357md8poejrw","ip_addr":"104.187.247.161","user_id":"hxwh3kazbff58p7ok46r5nx73y","method":"POST","err_where":"testEmail","http_code":500,"err_details":""}

When I set the security setting to TLS, I get the following error:

“Connection unsuccessful: Connection unsuccessful: unable to connect to the SMTP server through TLS: tls: first record does not look like a TLS handshake”

The following is in the log:

{"level":"error","ts":1624058873.0796726,"caller":"mlog/log.go:251","msg":"Connection unsuccessful: unable to connect to the SMTP server through TLS: tls: first record does not look like a TLS handshake","path":"/api/v4/email/test","request_id":"dhbow6di5tgctjsq7p1sz4jk1a","ip_addr":"104.187.247.161","user_id":"hxwh3kazbff58p7ok46r5nx73y","method":"POST","err_where":"testEmail","http_code":500,"err_details":""}

I’ve tried using both ports 25 and 587 - results are the same for both.

I would appreciate any help anyone might be able to provide because I’m just about out of patience with email…like all of it.