Why indeed? As it happens, this is quite a tricky question, since there are several variables at play. Getting your messages delivered to the spam folder can be really, really frustrating, but don't despair: you're not alone. From our extensive experience with successfully delivering right into inboxes, we've got some tips for you. Put these practices into action, and watch how quickly your delivery results improve!
To set the scene, a primary reason your messages are getting sorted into spam is the sorting and filtering processes of the recipient's mailserver. The options are limited to correct this solely from the Mailgun side, but you can implement the following to empower your sending's potential:
Have Recipients Safelist Your Domain
If the reason why your messages are being delivered to a recipient's spam folder is due to the server's settings, the quickest way to bypass this would be to invite your recipients to safelist your sending domain (found in your Mailgun control panel - make sure it's the exact one!). You could also have the recipient safelist the sending IP, however, this is really only advisable with a dedicated IP, since shared IP assignments are essentially dynamic; they could be changed automatically by our system without notification. Safelisting the sending IP should only ever be a secondary option to safelisting the sending domain!
Check Message Content
Spam filters take a large number of things into account that we simply aren't able to see, due to their security protecting their environment and users. What is well-known concerning these filters is that message content is extremely important. This is one element of the spam filtering puzzle over which you have direct control to help improve inboxing! The best way to determine what might be flagged in your messages would be to review them through a 3rd-party application to test just how "spamtastic" your content is in its current form, and what you can do to improve it.
Check DMARC Compliance
DMARC is very often a key element in the sorting mechanisms of ESPs (Email Service Providers). DMARC is all about ensuring the authenticity of a message and preventing spoofing. It helps demonstrate that a message has been protected by SPF or DKIM records; or, in the case of messages sent via Mailgun, both! However, it also indicates what should happen to a message if it does not pass the DMARC check - either mark it as spam, or reject the message completely! To ensure your messages pass the DMARC check with flying colors, you'll need to make certain the domains listed in the From, Sender, and Mail-From headers match each other exactly. That is, the domain listed in the From header is the exact actual sending domain.
For example, if your sending domain is ABCdomain.com, but your From field shows 123domain.com instead, you will almost certainly run into DMARC issues. Sometimes, even the difference between mail.ABCdomain.com and ABCdomain.com is sufficient for a server to place your message in a spam folder. We make sure that our Email Best Practices are clear that the domain listed in the From header and the actual sending domain should match for exactly this reason.
Lastly, we have a plethora of articles that are devoted to helping you improve those inbox rates; be sure to check them out! Here's a sampling that should get you started:
If any questions arise, just reach out to our Support team via the Support option in your Mailgun control panel!