I'm going to try allowing 587 and 2525 permitted above the Deny list. Thanks for the heads up!   Phil ... View more

Brandon,   Yes, we get NDRs from our SMTP sender.   Some examples: qq.com (China), gmail.ru, gmx.com (Germany), mein-florida-ferienhaus.de.    Our SPF records is setup correctly, else we couldn't send to Gmail, Yahoo, Office 365 mailboxes.   We have country (Layer 7) and specific IP (Layer 3)  address blocks in place.  Typically when we see something that looks suspicious incoming we block it.   Thanks, Phil   ... View more

And the issue we have is we can only send emails to North American systems.  Just about everywhere else in the world is blocked. ... View more

Thanks BrandonS.  After thinking about this a bit, I'm not even sure which ports we are actually using to send our outbound email.  Our SMTP sender is Microsoft IIS SMTP Virtual Service and it could very well be using other ports.   Phil ... View more

Thank you for your prompt reply.   Phil ... View more

Thank you for your prompt reply!   The objective is to allow our SMTP Sender (only, it doesn't have an inbound component) to be able to send to emails systems worldwide. Although we are a US based company, many of our customers use email systems in Europe and Asia, which we have blocked due to bad actors attempting to break into our systems.   Why do you say we shouldn't do this?   Thanks, Phil ... View more