Avoid Downloading Large Attachments in Mozilla Thunderbird

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You can stop Mozilla Thunderbird from keeping local copies of large messages in an IMAP account, or prevent their download entirely for POP accounts.

The Large Files People Send

You have so many friends. That some of them are special and some have peculiar habits is only to be expected.

So, of course, you have a friend or two that send huge attachments by email, say entire movies and oodles of pictures. Do you dislike waiting for these things to download when they only go to the trash anyway (unseen, mind you; that you love the people in your life does not mean you have to love the videos they shoot—or watch them—, does it)?

Avoid Storing Locally Large Messages and Attachments in Mozilla Thunderbird

To specify a message size limit and avoid downloading large emails and attachments in Mozilla Thunderbird for offline use:

  1. Click the Thunderbird (hamburger) menu button in Mozilla Thunderbird.
  2. Select Preferences | Account Settings from the menu.
  3. For IMAP accounts:
    1. Go to the Synchronization & Storage category.
    2. Make sure Don't download messages larger than ____ KB is checked.
  4. For POP accounts:
    1. Go to the Disk Space category for the desired account.
    2. Make sure Messages larger than ____ KB is checked under To save disk space, do not download.
  5. Enter the maximum size for messages you want Mozilla Thunderbird to download automatically.
    • The default 50 KB will let it download most messages that have no or just very small attachments but avoid almost all other emails with files attached.
  6. Click OK.

Mozilla Thunderbird will download messages as you open them but not keep copies offline.

Avoid Downloading Large Messages and Attachments in Thunderbird 0.9, Netscape and Mozilla

To prevent Mozilla Thunderbird 0.9, Netscape and Mozilla 1 from downloading large emails automatically:

  1. Select Tools | Account Settings... from the menu.
    • In Mozilla and Netscape, select Edit | Mail & Newsgroup Account Settings....
  2. Go to the Offline & Disk Space (for IMAP accounts) or Disk Space (for POP accounts) sub-category of the email account.
  3. Make sure Do not download messages locally that are larger than __ KB is selected.
  4. Enter a maximum message size.
    • The standard 50 KB are a reasonable value.
  5. Click OK.

Note that the message size limit is per email account. To apply it across the board, you have to set it for each account.

Mozilla Thunderbird, Netscape or Mozilla now truncate messages larger than the specified amount when downloading or going offline. Of course, you can download the full message if you like.

Download the Full Message on Demand

To download the full copy of a message only partially downloaded in Mozilla Thunderbird:

  1. Click the Download the rest of the message. link inserted at the end of the truncated email.

You can also delete the message right at the server without Mozilla Thunderbird downloading it in full.

More Ways to Save Space and Bandwidth

In Mozilla Thunderbird, you can set IMAP accounts to synchronize only a certain amount of time worth of mail, say the last five months. On the Synchronization & Storage settings page, make sure Synchronize the most recent is checked. You can also choose mail in which folders to keep offline: click Advanced under Message Synchronizing on the Synchronization & Storage settings page.

(Updated October 2015, tested with Mozilla Thunderbird 38)