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Paul Kroon
Asked: 2010-03-17 03:05:32 +0800 CST

Is there any limit on the number of e-mails in a given folder with Courier IMAP?

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I'm not running into a problem or anything, I was just curious about this when I saw I have 2 folders with around 20,000 items in each. Everything works fine (using Thunderbird), but I couldn't find anything with Google about this. Anyone ever heard of a limit on this with Courier IMAP?

imap courier

3 Answers

  1. Best Answer

    It depends on the file system:

    • FAT16: 512 per folder
    • FAT32: 65534 per folder
    • NTFS: 4,294,967,295

    In Linux, the limits are based on the number of inodes and the size of the drive. Note that ext2/ext3 and others that use the standard inode directory layout have a limit of ~32,000 sub directories in a directory.

    For 20,000 files, use a file system that stores files in a tree structure, rather than the list structure as used by ext2/ext3, UFS, FAT16/FAT32. You might also want to increase the size of the directory cache.

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  2. AFAIK there's no limit of mails per IMAP folder in Courier IMAP or the IMAP4rev1 specification.

    But the underlying file system on which the Maildir files are hosted could have a hard limit for the number of files per directory or at least may suffer performance degradation if a certain number of files in a single directory is exceeded.

    20,000 mails/files should not be a problem, though.

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  3. Just for other people's information here. I run an e-mail host and I've seen inboxes and mail folders with over a million messages in them. Granted, they are really slow and it causes other issues at that point with just loading the folder, but it will work eventually. I usually call people out after their inbox grows past 40,000 messages or so.

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