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Symptom

You are trying to connect to the mail server by IMAP and are seeing a message similar to „Maximum number of connections to this server reached“.

Cause

To protect a server from overusage by too many concurrent users, the number of connects that can be made at the same time using the same IP address is limited. Mail software normally creates up to five concurrent connections to a mailbox. The mail server allowes up to 32 concurrent connections from the same IP address. If seven end users connect through the same IP and all try to create several links to the server, so that that limit of 32 connections is reached, the server will block further connections.

Solution

32 concurrent connections to a mail server from the same IP are normally sufficient even for mid sized businesses, because not all end users access their mailboxes at the same time via IMAP. If the number of connections should still reach the limit, you need to decrease the number of concurrent connections. The number of concurrent connections can normally be configured in your mail software. For example, in Mozilla Thunderbird you can decrease the maximum number of concurrent connections of the work place to the mailbox from the default 5 to a lower value in “Server settings” -> “Extended” (“More options”).

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