Mail Loop
Also known as: Routing loop
A mail loop occurs when an email is forwarded back and forth between servers without ever reaching a final destination.
A mail loop happens when email routing configurations cause a message to circle endlessly between two or more servers. For example, if User A forwards their email to User B, and User B has an auto-forward rule back to User A, any email sent to either of them could get stuck in a loop.
To prevent these loops from crashing servers, email protocols have a "hop count" limit. Each time a message passes through a server, a counter is incremented. If this counter exceeds the limit (often 25 or 50 hops), the message is killed, and a bounce message (NDR) is returned to the sender, typically with a "Too many hops" error.
Mail loops are usually caused by misconfigured forwarding rules, aliases, or migration settings between on-premise and cloud environments.
Related Terms
Bulk Mail(Bulk Marketing)
Bulk mail is sending one email to a large group of people at the same time, usually without segmentation or deep personalization. It is a simple way to reach many subscribers with one message.
Learn more →Feedback Loop (FBL)(FBL)
A feedback loop is a system where inbox providers tell you when someone marks your emails as spam. It gives you a clear signal so you can remove complainers fast and protect your sender reputation.
Learn more →Abandoned Cart Email(Cart Abandonment Email)
An automated email that goes out when someone adds items to their cart but leaves without buying. These emails show what they left behind and usually include a direct link back to their cart. Most businesses send a series of 2-3 reminders over a few days, sometimes sweetening the deal with a discount or free shipping offer.
Learn more →Forward(Forward To A Friend)
When someone shares your email with another person by clicking forward in their email client or using a forward to a friend link in your email. It is a strong signal that they found your message useful, but manual forwards often break tracking so many teams prefer using dedicated forward to a friend features instead.
Learn more →