Description
I am using Mailer in Messenger worker long lived process with AWS SES SMTP interface and it keep throwing error:

Expected response code "250" but got code "451", with message "451 4.4.2 Timeout waiting for data from client.

I know i can get rid of this error by setting ping_threshold: 0 but it is not efficient since the transport have to ping server on every email sending out. It is better to manually stop transport connection when Messenger message get handled (with all emails are sent out) and it will auto start on next message handling. But the problem is SmtpTransport start & stop methods are private and i have no way to access them.