It may happen that certain sent or received emails no longer appear in your inbox or folders. This behavior can be explained by various technical causes. Below are the main reasons for this:
- Email address configuration settings on an email client:
When the configuration of an email account is changed from POP to IMAP (or vice versa), some sent or received messages may no longer appear in the inbox or in certain folders.
This behavior is explained by the way these two protocols handle email storage:
- The POP (Post Office Protocol) downloads messages from the mail server to a device (computer, smartphone, etc.) and, depending on the configuration, may delete them from the server after download. In this case, messages remain stored only on the original device and are no longer accessible via webmail or other devices.
- The IMAP (Internet Message Access Protocol), on the other hand, keeps messages stored on the server and synchronizes them across all connected devices.
As a result, if your account was previously configured using POP and has been reconfigured to IMAP, messages that were already downloaded via POP will no longer be present on the server and therefore will not appear in the new IMAP configuration.
For more information about email configuration protocols (POP / IMAP), please refer to the following detailed article: What is the difference between IMAP and POP?
- A filter or automatic rule has moved the messages:
Email clients allow users to create filters or rules that automatically sort messages based on specific criteria (sender, subject keywords, message content, etc.). These rules can then move, archive, mark as read, delete, forward, or even redirect messages—sometimes without the user realizing it.
Below are some indicators that messages may have been moved by a rule:
- Emails do not arrive in the inbox but appear in other folders such as Spam, Archives, a hidden or less visible folder, or an automatically created folder.
- Only certain emails disappear, not all of them, which indicates a filter targeting a specific sender or specific keywords.
- Emails appear briefly and then disappear, meaning a rule moves them shortly after receipt.
Filters or automatic rules often move messages without your knowledge. You should review your filters/rules, disable them if necessary, and check the Archives, Spam, All Mail, and custom folders.
- An antivirus may interfere with your email functionality:
An antivirus application may be responsible for the disappearance of certain messages from your mailbox, particularly if you are using an email client such as Outlook, Thunderbird, or the Mail application on a computer. Although this is not the most common cause, it can occur for several reasons.
Antivirus software generally monitors incoming and outgoing emails. It may determine that a message appears suspicious and block it, move it to a spam folder, or prevent it from being downloaded.
The antivirus may also flag attachments as suspicious and place the entire message in quarantine. In this case, the email will no longer be visible in the mail client but will instead appear in the antivirus security or quarantine section.
Additionally, antivirus scanning of IMAP or POP traffic can interrupt email synchronization. It may slow down or temporarily block the connection between the email client and the mail server. As a result, some messages may not appear or may fail to synchronize properly.
An antivirus can sometimes hide or block emails by filtering them, placing them in quarantine, or disrupting synchronization. In most cases, disabling email protection or checking the antivirus quarantine is sufficient to resolve the issue.