Emails can bounce if the recipients email server rejects the email and so it is blocked from being sent to the recipient. 

This may happen if the recipients email server runs spam checks and also DNS checks, for instance if SPF or DKIM records are not set up then the email can be rejected by the email sever - even if it is a valid email address. 

By checking the DNS (Domain Name System) we can see where we are actually sending the emails, in some cases emails are intercepted by an email checking service like mimecast or messagelabs.

 

These services generally block bulk emails – so our suggestion would be to look at the content of your email campaign to make sure that there is nothing spam like in there which could cause your email to be intercepted. 


The recipients email server may also look at the IP addresses of the email server that the email is coming from - if the IP address is found on a blacklists then this can be why the recipients email server rejects the email and so it is blocked. 

 

We would also advise that you contact the email recipient that you are in regular contact with to ask them to ‘whitelist’ your senders email address as a trusted source.