The problem with missing e-mails that someone sent to you but you never received, or those you sent but were not received by the recipient, can be perplexing. Here are some of the explanations we have seen for missing messages.
E-mail is an unusual web service because messages can literally vaporize and disappear forever if the proper connections are not made between the sending and receiving mail servers. A lot of this depends upon how the servers are configured. Many SMTP (this system sends messages) servers will periodically try to resend messages if they cannot connect to the receiving server–but not all are configured to do this.
Some ISPs trim and delete messages that their systems flag as spam. This is usually due to suspicious spammy words in messages or an IP address or e-mail address that is on a spam blocklist. We did a study a few years ago that revealed how major ISPs deal with suspected spam. Some would delete the message entirely (AOL), and others would snag them in an online spam bucket (GMail, Yahoo, Hotmail, MSN). The most unusual was Cox because they removed paragraphs from messages that contained trigger words such as “free”. None of the ISPs in our tests informed the recipients of the changes, spam snags or deletions.
While most users who download messages via POP3 or IMAP do check local spam filters on their PC set up by Thunderbird, Outlook, or other e-mail clients, they frequently forget to check the spam holding areas in online services. GMail, Hotmail and most free e-mails services are notorious for grabbing legitimate messages and holding them online as spam. The e-mails never make it to the users’ PCs. You will find the missing messages by logging into the online e-mail system and checking to see what is flagged and held as spam. Online e-mail accounts do usually have methods to flag messages held as spam as “not spam”. If you are missing messages, log into your e-mail service or ISP’s online system to see if the messages were snagged there. Flagging legitimate messages as “not spam” releases the messages so they can be downloaded.
Keep in mind that there are two possible spam buckets. One is with the e-mail service’s online account; the other is on your PC if you use an e-mail client that includes spam filtering features.
When sending messages to large groups of people, make sure that you are not exceeding your ISP or hosting company’s daily limits. Many ISPs and hosts set a daily message limit in order to prevent spammers from sending messages to thousands of recipients using a large list. Most limits are generous, but some ISPs set a limit of 10 recipients per message. The limits the apply can be total recipients per message or per day. GMail allows 99 recipients per message or 2000 total messages sent per day. When the limits are exceeded, outgoing e-mails are simply deleted.
What to do if you are not receiving messages
if you do not find a missing message held in a spam bucket in the e-mail client you use on your PC, log into the e-mail service’s online system. Release any legitimate messages held there by acknowledging that they are not spam. Most systems also have a White List feature. A White List contains the e-mail addresses from senders that are always legitimate. Adding an e-mail address to a White List should assure that the message bypasses any spam filters and will always come through.