WHM with SES Services problem

I m using WHM service in Lightsail. I have many domain name in this server. I m using SES to relay the mail. the first question, some user send email with error message "message has lines too long for transport" the second question, some email can't do forwarder. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: XXXXX@gmail.com host email-smtp.ap-southeast-1.amazonaws.com [XX.XX.XX.XX] SMTP error from remote mail server after end of data: 554 Message rejected: Email address is not verified. The following identities failed the check in region AP-SOUTHEAST-1: cpanel@XXXXX.com, "cPanel on XXXXX.com" cpanel@XXXXXX.com

what's the solution of this case? is it buy a Dedicated IP to slove this problem?