Error Codes

SMTP Response

SMTP Responses provide a brief explanation into the reason behind why your mail was not delivered. All response codes / subcodes must comply with relevant RFC specifications among different mail providers making it easier to fix issues. Error codes fall into two main categories : Deferred (4xx) and Rejected (5xx) these codes show us what is causing your temporary or permanent issues and enable you to fix these errors or issues

Deferrals (4xx Codes)

A 4xx error indicates that there is a temporary failure, this means mail cannot be sent at the current time, the best thing to do with these issues is to wait a while and try to resend your email later. An example of what can cause these temporary failures would be if your mailbox was receiving too much mail in a short period of time, this means the servers need to catch up with processing the mail.

Rejections (5xx Codes)

A 5xx error indicates a permanent failure. This error indicates an error in your emails content, formatting or recipients that prevents delivery. These issues must be addressed and edited before re-attempting delivery. The error contained in the SMTP response will indicate the specific problem with the message. For example if you are trying to send an email to an inbox that does not exist.

Deferral Codes

Connect

SMTP Code SMTP SubCode Support Code Bounce Message
421 G2 "Too many concurrent
connections from this client (G2)"

Too many concurrent connections from client IP
450 4.7.1 G1F "4.7.1 Client host {IP}
has no PTR record (G1F)"

We require that incoming IPs have a valid PTR

RCPTTO

SMTP Code SMTP SubCode Support Code Bounce Message
450 4.4.1 G6 "4.4.1 {EMAIL}: The
recipient's server was temporarily unavailable to accept your message
(G6)"

A temporary failure while attempting to verify the recipient address

DATA

SMTP Code SMTP SubCode Support Code Bounce Message
450 4.4.6 G16 "4.4.6 Routing loop
detected (G16)"

An undeliverable mail loop was detected
450 4.4.0 G1E "4.4.0 {EMAIL}: Temporary
DMARC DNS lookup failure (G1E)"

A temporary failure while looking up sender's DMARC policy

Rejection Codes

SMTP Code SMTP SubCode Support Code Bounce Message
550 5.1.1 G8, G9 "5.1.1 {EMAIL}: Email
address could not be found, or was misspelled (G8, G9)"

Recipient address does not exist on our system
550 5.7.1 G3, G4, G5 "5.7.1 Virus found
(G3,G4,G5)"

Message was identified as a virus by our content filter
550 5.7.1 G15 "5.7.1 Email rejected per
DMARC policy for {DMARC DOMAIN} (G15)"

Message failed DMARC validation
SMTP Code SMTP SubCode Support Code Bounce Message
550 5.7.0 G18 "5.7.0
header_contenttype_1 (G18)"

Rejected for matching a known virus signature
550 5.7.0 G19 "5.7.0
header_contenttype_2 - Multi-part MIME messages are rejected as dangerous
(G19)"

Partial MIME messages are not supported
550 5.7.0 G1A "5.7.0 mime_banned_file -
Your message has been rejected because it contains a banned file attachment
(G1A)"

Executables in compressed attachments are not allowed
SMTP Code SMTP SubCode Support Code Bounce Message
550 5.7.0 G1B "5.7.0 mime_banned_file -
Your message has been rejected because it contains a banned file attachment
(G1B)"

File Types that exploit vulnerabilities in Windows programs are not
allowed
550 5.7.0 G1C "5.7.0 mime_banned_file -
File attachment is not allowed because they can be used to exploit Winzip
(G1C)"

Messages with attachment file extensions linked to WinZip vulnerabilities
are not allowed
550 5.7.0 G1D "5.7.0 mime_banned_file -
CLSID file extensions are dangerous (G1D)"

Messages with attachment file names containing Windows classIDs are not
allowed

RCPTTO

SMTP Code SMTP SubCode Support Code Bounce Message
550 5.7.0 G1A "5.7.0 mime_banned_file -
Your message has been rejected because it contains a banned file attachment
(G1A)"

Block messages with .exe files in attached archives

DATA

SMTP Code SMTP SubCode Support Code Bounce Message
550 5.1.1 G8, G9 "5.1.1 {EMAIL}: Email
address could not be found, or was misspelled (G8, G9)"

Recipient address does not exist on our system
550 5.7.1 G7 "5.7.1 {EMAIL}: The
recipient's server refused to accept your message (G7)"

A permanent failure while attempting to verify the recipient address
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