Errors in SMTP dialog

The Selectel mail service uses the SMTP protocol. The following SMTP dialog errors may occur when sending mail from your server to the mail host of the service.

`550 bounced check filter`	The email address of one of the recipients is in stop list. If more than one recipient is specified in the e-mail, repeat the sending for each of the recipients separately. If the address is in the local stop list, you can find and delete an address from the local stop list
`501 from domain not trusted`	The domain from which the email is being sent has not been added to the list of allowed senders. Make sure that the correct connected the service for the domain
`421 SMTP command timeout — closing connection`	The server closed the connection because it has not been used for more than 120 seconds. To clear the error, start the SMTP dialog again