holds the emails without any NDR

Copper Contributor

Hi Dears,


I hope you're doing well. I have an issue and am asking you to help me to find a resolution. Any help is appreciated.


We are working with other companies and send emails every day to them with different types of attachments like .xlsx, PDF, etc. 

Some of these companies are hosted by for their email service and we have this issue there.

All of them that are hosted by can not receive our emails. holds our emails in the queue and doesn't deliver our emails to the recipient. It happens just for emails with any type of attachments. All emails without attachments will be delivered. Also, outlook doesn't send us any NDR email or answer with information, why it holds the emails in the qeue.

We use another smart spam service (ProofPoint) and all these emails are considered as clean and delivered to the destination. (

All brands that are hosted by hosting services other than receive the same emails without any issues.

Additional info is that we have all the necessary security items like DMARC, SPF records, etc and I checked our IPs in the Blacklist of spam checkers.


I appreciate any help or information which helps us to find the reason for this problem.


Many thanks,

Kind Regards,





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