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Problems with sending emails to some mail servers
that refused to accept your mails without
MX record
  Most common reason for undeliverable mails
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Page 1> MX records or Mail Exchangers

This Page 2>
If there are no MX records?

If there are
no MX records for the receiving mail server will terminate the connection after the initial HELO command (or delete it after accepting).

If the beginning HELO command argument is not acceptable a 501 failure reply must be returned. If the commands in a transaction are out of order a 503 failure reply must be returned. See: How Email Works and How does my email gets to the recipients?


Command - a request for mail service action sent by the sender SMTP to the receiver SMTP

If there are one or more MX records associated with the domain the receiving mail server then determines if the sending mail server is one of those machines listed with MX record. If not, the receiving mail server will not accept mails after the initial handshaking HELO command (or delete it after accepting).

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If (the sending mail server) is listed as a valid mail server for the domain in question, and a reverse nslookup of the IP address name also associated with that IP address, for example:

The owners of that IP address matches the name of the sending server ( only then, will the receiving mail server accept any inbound mails—what it mean is that your emails will be rejected by the recipient mail server if any one of these conditions are not met:

1. Your mail server (ie: do not have a valid name?

2. Your mail server (ie: do not have MX records for the domain?

3. Your mail server (ie: do not matches correctly via a reverse DNS lookup?

To reduce spam, many ISP mail server perform a reverse nslookup to validated the sender, nslookup - a DNS tool that Perform forward and reverse DNS queries for the current address to get the hostname of an IP address.

If your mail server IP address is (an internal IP address) your mails are considered spam-and will be rejected and becomes undeliverable in your mail server outbox or, it may be accepted and deleted without the sender being notified (this way  spammers will think that their mail got through).

Therefore, the solution is to change the way your mail server computer identify itself to the remote mail server.

If you find that sending emails to AOL, Hotmail, Yahoo, and other similar Web-based email accounts does not work. Try changing the way your computer mail server identify itself to the remote mail server.

Most mail server program allows you to change "Server identity" for the HELO handshaking command.

For example, if your email address is set the HELO handshaking command identification to or try it with just only: Notes: Use your own domain address and not the above examples.


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Notes: Sending emails with the FROM: field email address that is different from the login IP address or not using an actual IP address may also result in having mails being rejected by the recipient mail server. If you are using a router, try using your router IP address.

Many ISPs like Yahoo, Gmail, Hotmail, AOL, etc., are known to check the sender email domain name, for example: against the HELO address during the handshaking identification.

Therefore, if you are using a Hotmail or Yahoo email address (at the FROM: field as sender address), your email will be rejected even though the FROM: field clearly identifies the sender.

Many ISPs do a reverse DNS lookup to ensure that the SMTP mail server that is requesting to send a message actually exists as well as the email domain and IP's MX record and if there isn't one, mails are rejected or deleted as spam.

Every ISP have their own standards and ways to filter spam, therefore, by clearly identifying yourself at the FROM: field for most web-based email recipients like: Hotmail, Yahoo, Gmail, etc., may not work with many ISPs as well as the other way round.

You may need to segregate your email address list, as well as to keep in mind that ISPs also limits accessibility to their mail server by time and quantity of mails. Therefore, you may need to experiment a bit by using a combination of different strategies for different popular web based email recipients.

Most of the time, it is usually due to your mail server identifying itself as an internal mail server IP address which can be simply solved by using an actual exact IP address.

IP address is numeric numbers, for example: and not See: Most common reason for undeliverable mails

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