FAQs

Why Is My Email Being Rejected?

Firstly, this guide is intended for those who are sending emails to our customers, but they are not being received or they are being rejected by our mail servers. It is not a guide to our customers who are having problems sending onwards.

At Coolmail, we consider the quality of our customer’s emails to be very important. As such we check incoming email for viruses and unsolicited commercial emails (spam). An email which carries a virus is automatically rejected. Full stop. No exceptions.

In order to protect our customers from spam, we make a series of checks and reject mail based on many different criteria. We don’t attempt to check the content of emails at present, as genuine spam senders change their content very regularly to avoid being detected in this manner. Instead we make a series of checks on the mail server which is attempting to send mail to one of our servers before accepting email. All of the techniques we use are aimed at reducing spam email as they are detecting errors commonly made by bulk emailers, but almost NEVER made by a reputable ISP.

If your email is being rejected for some reason, then it’s very likely that you will have trouble sending mail to any other service provider who protects their customers in this manner, and you should seek to remedy the problem at YOUR END!

To assist you in this, we have a list below of how we filter our emails for spam and why we do each one. You’ll also find how to correct your problem, even if you don’t like the solution!

1. Recipient must exist on our servers.

Obvious really! We don’t accept mail which is destined elsewhere other than from our own clients. Try checking the email address you are sending to does exist and is correctly spelt.

2. Your declared email address is in the wrong format.

Our customers couldn’t respond to you if your email address is not in a suitable format. E.g. “fred@.com”. Check your email client software and ensure that your email address is filled in correctly.

3. Your email address has a domain part that has no means of receiving email.

Again, customers could not respond to you if the domain either does not exist or has no path to return the reply. E.g. “fred@nowhere.com” when the domain “nowhere.com” does not exist. Check as above.

4. The server sending email to ours is listed as being an open relay.

An open relay is a server which will accept email from anyone going to anyone. They are exceedingly badly configured. These systems are a magnet for spammers as they allow them to send to the rest of the world undetected. If your ISP has a mail server in this list, be VERY worried. If it’s your own mail server, FIX IT!

5. The sending server is listed as a known sender of spam emails.

Speaks for itself really. Reputable ISPs keep a check on their senders and recommend their customers to send email via the ISPs servers to allow this. Such ISPs (ourselves included) are likely to terminate your account if you send spam. Some ISPs really don’t care what their customers do and often end up with their servers in this type of database. Any ISP who deliberately allows this to continue has no consideration for their genuine users who then can’t send email to filtered systems. If this happens regularly, change your ISP to a better one who DOES care about you. If you run your own mail servers and you are in this list then you are a spammer and we don’t want your email anyway.

6. The sending server is listed as a known dynamic IP.

Certain IP addresses are deliberately listed by the ISP as being dynamic and hence not to be trusted as genuine email senders. These are IP ranges allocated to their customers for their connection. Although this may seem strange, it is used to block customers who have compromised (usually a virus) systems from sending out email directly. Your ISPs policy will be to send your emails via them for forwarding where they can check for spam, viruses, etc. They will have overridden the check against your IP address and domain name to allow this. This is a common problem for those using their own mail server; if your ISP has entered your allocated IP as dynamic, then you MUST send your email via their mail server, NOT directly!

7. The sending server didn’t say hello.

Actually it should say “HELO”. This is the correct manner for a mail server to introduce itself and present who it is. Spammers will usually avoid introducing their systems as then it can’t be checked for other thing such as its declared name etc. Your ISPs mail server will ALWAYS say hello, if you are using your own mail server and it’s not doing so, then you need to get it configured properly.

8. The sending server doesn’t know its own name.

Spammers often declare their systems to be something other that what they are. Once more, your ISPs mail server will know who it is. The mail server should declare itself as “hostname.domain” e.g. “mail.yourisp.com”. If you are running your own mail server then make sure it knows who it is and that the syntax is OK.

9. The sending server declares itself to be at an unknown domain.

Another spam trick. Spammers declare a server name but it’s not a real domain. Your ISP will get this right; your own mail server could have a misspelling.

10. The sending server has no return path for mail.

The spammer uses a real domain, but the domain has no mail record to send emails back to it. Your mail server must belong to a domain with an MX record. Fix it.

11. The sending server claims to be our server.

Oldest trick in the book! Early mail servers would always accept mail from themselves, so the spammer’s mail server declares itself to have the same name as ours e.g. “mail.coolmail.org.uk”. Sometimes they try other similar attempts such as claiming their name to be our IP address. Sorry spammers, we don’t fall for this one.

12. The sending server gives a valid name, but this doesn’t tally with its IP address.

This is the BIGGEST cause of bounced emails. Spammers will use a machine at one IP address whilst claiming in the introduction to be another server at a different IP address. MANY mail servers fail on this one, but your ISP won’t make this mistake. If you have your own mail server and send out mail directly, then your mail server MUST have an A record and a PTR record which match. Let’s say your mail server is called mail.yourdomain.com (its hostname) and it is on an IP address of 85.91.232.97 (actually that’s one of ours). Then a DNS lookup of that IP MUST return the same hostname. Many small to medium companies set up a mail server on their ADSL broadband connection and then give a meaningful (and accurate) name to the mail server by which it declares itself. They then forget that the ISP providing the line will have assigned a name to the IP address (usually one which reflects the IP address and the ISP name). If your mail is being bounced this way then set your mail to send out via your ISPs mail server.

OK. There you have it. If you can’t send email to one of our customers, then the problem is at YOUR end. Either you’re not playing by the agreed rules (the above are only some of them!) and need to reconfigure your mail server or your ISP really doesn’t care about you.

If your ISP doesn’t care, how about signing up with Coolmail for a business quality service?