Error: Could not complete sender verifyThis is a common issue which happens when using the cPanel username for authenticating on the smtp server. Please use the email username instead and this issue will be resolved.
For more information please check our Mail tutorial:
http://www.siteground.com/tutorials/email/index.htm
_______________
Find expert web hosting services at SiteGround.com - unlimited email accounts, unlimited forwarders, webmail access from anywhere, POP3, IMAP, SMTP.