5.3.0

Message Not Delivered: unknown issue with the receiving system

The message could not be delivered because of an unknown problem with one or more of the recipients' email systems.

Fixes

Double check that the recipient's email address is correct. Wait a few minutes, then try sending the message again.

If necessary, contact the recipient(s) another way (e.g., phone or text message) to confirm their email address.

5.3.0: Official Definition

5.X.X

[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that start with 5.X.X:

A permanent failure is one which is not likely to be resolved by resending the message in the current form. Some change to the message or the destination must be made for successful delivery.

X.3.0

[RFC3463] (Standards Track) from the The Internet Engineering Task Force (IETF) definition for codes that end with X.3.0:

The destination system exists and normally accepts mail, but something about the system has caused the generation of this DSN.

Assess

Sender Score

The original. Monitor your sender reputation.

Blocklist Lookups

See if you’re on the Return Path Blocklist.

List Quality Checks

Upload your list to see if your contacts are legit.

Deliverability Benchmarks

Compare your stats to the global email community.

Email Revenue Calculator

See the revenue potential of your email campaigns.

Bounce Lookups

Find out why are your emails bouncing.

Learn

Podcasts

See what's new and what’s next in the world of email.

Courses

Deepen your sending knowledge.

Email Insights

Curated learnings and hot tips from the email community.

Act

Subscriber List Analyzer

See a breakdown of your subscribers’ mailbox providers.

Subject Line Previewer

See how your subject line will appear in the inbox.

Complaint Monitor

Blocklist Remover

Improved your sending behavior? Ask to be removed from the Return Path Blocklist.