Common Reasons for Email Deliverability Issues


In this article we will explore the common issues that can impact your email deliverability and how you could solve them. 


IP Warming

Mailbox providers are suspicious of emails coming from an IP that has no reputation or that has an unfamiliar sending pattern. IP warming is the practice of gradually increasing the volume of mail sent with a dedicated IP address according to a predetermined schedule. This process helps to establish a reputation with inbox providers as a legitimate email sender. If you immediately begin sending large amounts of mail, you will risk having your messages blocked by inbox providers.


Mailbox Security Features

Our external mailbox provider has two main security features that may impact deliverability, DMARC compliance and DNS SPF. 

A sender policy framework (SPF) record is a type of DNS Text record that lists all the servers authorized to send emails from a particular domain. For emails to reach your mailbox a valid SPF record must exist for the sender address on the SMTP server it has been sent from. 

DMARC is an email validation system that helps ensure that emails are sent only by authorized users. DMARC policies dictate what servers should do with emails that fail SPF and DKIM checks. In the case of our external mailbox provider, emails that fail a DMARC compliance check are rejected. 

Both of these security headers are present in each email you send and can be viewed by examining the HTML headers of an email. This can be done using a text editor.


Receiving limit: 400 messages/10 minutes

Our external mailbox provider has a limit in place for how many emails can be received by a mailbox within a 10 minute period. If a mailbox receives over 400 messages in this period, any additional messages will be deferred.

Email senders will typically retry a deferred message at least once, possibly resulting in the message being delivered after a short delay. This will vary for each sender and may be something that is mutable. 

To avoid this issue entirely we advise spreading the time your backups report across the day.


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