Web hosts often get complaints from clients that they are not receiving mail properly. Their complaint is that if specific persons send them a mail from specific email addresses, their mails bounce with an error message. This means that the mail is not delivered and rejected by the server. More than 90% of such complaints are due to an issue from the sender’s side. This article tries to highlight the possible reasons why a specific set of senders are not able to send you email.
Spelling errors are one of the most common reasons why a persons mail may not be reaching you. A friend was once complaining to me that my work email address kept bouncing, wheres when he sent me a mail on Gmail it went through smoothly. On inspecting the bounce back mail, it appears that the friend had saved the wrong spelling of my work email address and that’s why it was bouncing. Although this point may seem frivolous, it is one of the most common reasons of mail bouncing, especially when sent for the the first time to a new email address. Before diagnosing any mail server issues, you should inspect the bounce message to determine is the username or domain name in the email address is correct and reachable. Another common issue is having a mailbox which has exceeded its storage quota. Any mails received when the mailbox was full, will bounce back to the sender.
Some people specifically setup mail filters to prevent certain types of mail from reaching them. You can setup a mail filter to discard any unwanted mails which contain a certain word or certain email address. This can lead to false positives and any type of mail matching that criteria to be filtered out. Mail filters can be setup to send a bounce message or to silently discard the message without giving a reply. If there is no bounce message, then you may want to check the mail filters.
An important reason for mails bouncing is when the content of the mail is suspicious. If the mail contains too many trigger words like FREE FREE FREE or dollar signs like $$$$ or contains numbers indicating millions of dollars, then the spam filters flag the mail as spam and may bounce the mails. Similarly, if the email body contains too many links or URL’s to external websites, the mail mail also be considered to be spammy. Most mails that will be blocked are genuinely spam mails, however, the filter may also catch false positives i.e. genuine mails which may be considered suspicious. An amusing example was of a client who was unable to receive mail from a sender whose name was Ms. Loan. Although it was a perfectly legitimate mail which was requested by the recipient, because it contained the word Loan and because it had a reference to various hyperlinks and because it contained information about how much money was to be transacted, the mail was marked as spam and bounced.
Most email providers use blacklists to determine if a server sending mail is a legitimate one or has been engaged in any spam activity recently. These blacklists are maintained by third parties who update them regularly i.e. in real time. Hence, these are called RBLs or Real Time Blacklists. Once a domain name, IP address or email address is in one of these, most of their mails to many mail servers across the world will bounce, due to their mail being detected as possible spam. Usually a bounce mail with the error message will be generated, providing a reason for rejection. However, some spam filters silently destroy the mails without letting the sender know why it was happening.
We all like to publicize our business and credentials in our email signature. But some people just overdo it. While images and phone numbers are fine, some people tend to stuff the signature with several URLs and try to make a design using special characters. Such type of signatures are treated with suspicion and may set off the triggers to block mail.
There are numerous online tools which can test the spamminess and legitimacy of your email headers and provide a perspective on how the mail filters might see them.