Forwarders that point at each other cause mail to circulate until the server stops it.
HOW LOOPS HAPPEN
info@ forwards to sales@, and sales@ forwards to info@ A forwarder points at an address that forwards back to the original domain An autoresponder replies to an address that autoresponds in turn A forwarder points at a mailbox on another server that forwards back
WHAT YOU SEE
Mail never arriving, bounces mentioning a loop, or a sudden burst of duplicate messages.
FINDING IT
cPanel > Forwarders lists every forwarder on the account. Read the list and trace each destination.
Check autoresponders too, and any rules set inside webmail.
PREVENTING IT
Keep forwarding chains to one step. If info@ should reach three people, forward to three mailboxes rather than through a chain. Do not forward an address to itself, which is easier to do than it sounds when editing. Set an interval on autoresponders so they cannot reply repeatedly to the same sender.
WITH EXTERNAL ADDRESSES
Forwarding to Gmail, where Gmail forwards back, is a common cause. Avoid two-way arrangements.
