Senders see a “550 relay not permitted” error when they try to email me.
When someone sends you an email they might receive a bounced back message, that has the following error inside it:
550 relay not permitted!
SiteGround uses SpamExperts to filter incoming emails, and the error above means that your domain name is not properly routed in the incoming SpamExperts configuration. While it is not expected, this problem can occur when moving your account or website between servers, or when you enable or disable the SpamExperts incoming service.
This is something that the SiteGround advance technical team can help with.