ESN . POSTMASTER

Extra Security Networks

Recipient

554 5.7.1 : Relay access denied
Domain: We do not handle the email for this domain or user

550 5.1.1 : Recipient address rejected: User unknown
Mailbox: The mailbox or user does not exist

450 4.1.1 : Recipient address rejected: unverified address: mailbox full or unavailable
Mailbox: The recipient mailbox is full.

Sender

450 4.1.8 : Sender address rejected: Domain not found
The domain part of the "from" or "reply to" email address does not exist, or can not be resolved on the public internet

521 5.7.1 : Sender address rejected: ip location rejected <text>
The domain part of the "from" or "reply to" email address does not normally send from the source IP address.

521 5.7.1 : Sender address rejected: ip location rejected <text>
The domain part of the "from" or "reply to" email address does not normally send from the source IP address.

Helo or Ehlo

521 5.5.2 : Helo command rejected: need fully-qualified hostname
A fully qualified domain name (FQDN) is required in the helo\ehlo greeting. The sending server is sending a helo\ehlo like "mail1" or "mail1.local", rather than a FQDN of "mail1.foo.com".

550 5.7.1 : Helo command rejected: Host not found
Helo does not resolve: The FQDN provided in your helo\ehlo greeting does not resolve to a public IP address.

554 5.7.1 : Helo command rejected: dynamic IP addresses prohibited
We do not accept email from dynamically assigned IP addresses. Please obtain a static IP address from your provider, or relay your mail through your provider's mail server.

554 5.7.1 : Helo command rejected: residential IP addresses prohibited
We do not accept email from residential class IP addresses. Please obtain a static IP address from your provider and configure proper (non-generic) FcrDNS.

554 5.7.1 : Helo command [text] blocked using xxx [more text]
One of the Realtime Block Lists (RBLs) that we use, does not like some aspect of the helo\ehlo greeting that your server has sent. Please see the specific RBL text in the error for more information

521 5.7.1 : Helo command rejected: your email has been rejected
The sending server has sent spam or unsolicited email to one or more mailboxes on our network. Email will not be accepted from this host.

Sending Server (client)

450 4.7.1 : cannot find your reverse hostname
Reverse DNS: The IP address of the sending server does not have a reverse DNS (PTR) record.

450 4.7.1 : cannot find your hostname
Reverse DNS: The IP address of the sending server has a reverse DNS (PTR) record. But the host name provided in the rDNS either does not resolve back to an IP, or resolves to a different IP.

554 5.7.1 : Client host rejected: Generic rdns prohibited
Reverse DNS: Generic reverse DNS entries such as "10-133-54-76-static.some.isp.net" are prohibited. Please contact your provider and have them set the rDNS entry for your mail server IP to a domain name that you directly control, and a host name that clearly identifies ths server as a mail server.

550 5.7.1 : Client host rejected: [host name] does not resolve
Reverse DNS: The IP address of the sending server has a reverse DNS (PTR) record. But the host name provided in the rDNS does not exist or resolve back to any IP.

554 5.7.1 : Client host rejected: dynamic IP addresses prohibited
We do not accept email from dynamically assigned IP addresses. Please obtain a static IP address from your provider, or relay your mail through your provider's mail server.

554 5.7.1 : Client host rejected: residential IP addresses prohibited
We do not accept email from residential class IP addresses. Please obtain a static IP address from your provider and configure proper (non-generic) FcrDNS.

554 5.7.1 : Client host [text] blocked using xxx [more text]
One of the Realtime Block Lists (RBLs) that we use, does not like some aspect of the sending server. Please see the specific RBL text in the error for more information

521 5.7.1 : Client host rejected: your email has been rejected
The sending server has sent spam or unsolicited email to one or more mailboxes on our network. Email will not be accepted from this host.

521 5.7.1 : Client host rejected: spam source
IP address rejection. The IP address of the sending server has sent spam or unsolicited email to one or more mailboxes on our network. Email will not be accepted from this IP address.

521 5.7.1 : Client host rejected: spam 20xxxx
IP network rejection. The IP network that contains the IP address of the sending server, has repeatedly sent spam or unsolicited email to one or more mailboxes on our network, from many IP addresses within said network. Email will not be accepted from this IP address, or any address within the IP network

521 5.7.1 : Client host rejected: server ip location rejected, only accepts <text>
The mailbox or user does not accept email from your geographic location.