Emails not getting delivered to

A customer asked a question about email not being delivered to a inbox from sendgrid.

we are trying to send mails through our application to Mailsac but those emails are getting blocked, with reason “554 Sender Denied” When we reached Sendgrid support team on this issue they suggested us following resolution ,

“In order to resolve these type of blocks you`ll need to reach out to the sys admin of the recipient domain that you’re sending to ( and have them change a setting on their spam filtering to look at the from address instead of the return path address.”

Request you to change spam filtering so that messages can deliver to

Our technical team does use a denylist in order to ensure system availability for our customers. Incoming emails may be denied for based on a several factors, but not limited to IP address, domain, and email address.

If you are unable to send to or a domain hosted on and you are receiving a 554 Sender Denied error, your email is being denied because of our deny list.

For customers on Business or Enterprise plans, we can add your sending domains or IP addresses to our allow list.

For customers on our Basic or Indie plans, I recommend posting on the forums and we will provide assistance regarding why messages are not being received.