Formatted HTML emails deleted by ISP mail filtering system

ISP mail server perform a reverse nslookup to
validated the sender, therefore, if your mail server
IP address is an internal IP address your mails are considered spam

Mail Servers FAQs
If you are using your own mail server program to send emails the most common problems for undeliverable mails are identified here, please go through them carefully and it will solve most of your problems.

	Most common reason for undeliverable mails
	Open Relay and Blacklist
	MX records or Mail Exchangers

About MX or Mail Exchangers

MX or Mail Exchangers are database records (registered domains in the "server identity" bank) particulars of domain names of mail server running with SMTP responsible for a domain or a block of domains.

SMTP servers (including your mail server) works like this: When the mail server received an email for me@mydomain.com the mail server will check and see if mydomain.com is a domain that is served by it and then, deliver the email to the mailbox for me@mydomain.com

Notes: Mail server received--refers to the recipient mail server (when you send-out an email) and refers to your mail server (when someone sends you an email).

If mydomain.com is not served by this particular mail server (ISPs usually have more than one mail servers running) then the mail server looks for mydomain.com MX records. If there are no MX records for it, the mail server will attempt to deliver the email directly to the computer at mydomain.com (if the mail server is up and running) will accept the email--if there are MX records the mail server will attempt to deliver emails to the mail server pointed by the MX record.

Normally, to send and receive mails, you do not need to have an email domain with MX records because your email domain name will be pointing directly to your (if it is up and running) mail server.

If you are having problems getting or sending mails, or because some ISPs, to prevent unsolicited (spam) bulk emails--See: Email Filtering--may blocked or delete your mails from being delivered to intended recipients within their domain. If that is the case, you will have to contact your ISP (managing your DNS block of IP domains) which your email domain belongs to and ask them to keep an MX record that point to your mail server computer.

Problems with sending emails to some mail servers that refused to accept your mails without MX record

Normally, mails are sent to a specific email address domain mail server and if your mail server program have an option for "Force Delivery or Aggressive Verification"--then;

It should be able to detect (in real-time) a few others different available MX records mail servers within the recipient ISPs and will attempt to deliver mails to them. Meaning that; your mail server program should detect all MX records addresses obtained from your recipients ISP block of DNS server domain and attempt to deliver mails to all of them.

If your emails are blocked and can't be delivered to some of your recipients ISPs, options available are; Ask your ISP to keep MX record pointing to your mail server computer or to use email domains that have registered MX record addresses (registered domains in the "server identity" bank).

For a list of Internet Service Providers with MX record that you can sign up:

www.emailaddresses.com/
www.isps.com/
www.thelist.com/
www.findanisp.com/

Many ISPs mail server, ie: AOL, Yahoo, Hotmail, Juno, etc. uses technique to prevent unsolicited bulk emails (SPAM) from getting to their users.

When a mail server ie: yourmailserver.com initiates a session with a HELO command, the receiving mail server performs a reverse nslookup of: yourmailserver.com and check if the sender mail server domain has MX records.

If there are no MX records for yourmailserver.com the receiving mail server will terminate the connection after the initial HELO command (or delete it after accepting).
See: How Email Works

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

If there is one or more MX records associated with the domain yourmailserver.com the receiving mail server then determines if the sending mail server yourmailserver.com 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).

If yourmailserver.com (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, ie: the owners of that IP address matches the name of the sending server (yourmailserver.com) only then, will the receiving mail server accept any inbound mails.

Meaning that: Your mails will be rejected by the recipients mail server, if any one of these conditions are not met.

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

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

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

To reduce spam, many ISP mail server perform a reverse nslookup to validated the sender, therefore, if your mail server IP address is 127.0.0.1 (an internal IP address) your mails are considered spam--will be rejected and becomes undeliverable in your mail server outbox--or, it may be accepted and deleted without being notified. 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 me@myserver.com set the HELO handshaking command identification to mail.myserver.com or try it with just only: myserver.com Notes: Use your own domain address and not the above examples.

Notes: Sending mails 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.

AOL is known to check the sender email domain name, for example: from@mycompany.com 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), AOL will reject the mail even though the FROM: field clearly identifies the sender.

AOL also does a reverse DNS lookup to ensure that the SMTP mail server and 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 has 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, etc., may not work with AOL or other ISPs or 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 127.0.0.1 which can be simply solved by using an actual exact IP address. IP address is numeric numbers, for example: 151.196.75.10 and not mydomain.com
See: Most common reason for undeliverable mails

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nslookup - a DNS tool that Perform forward and reverse DNS queries for the current address to get the hostname of an IP address.

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