edmullen dot net

MOZILLA MAIL SYNC - Considerations when using two PCs to access the same email account

This page discusses the issue of using multiple computers to access the same email account. It only applies to POP (Post Office Protocol) mailbox services provided by most ISPs (Internet Service Providers), not IMAP, and a Microsoft Windows XP installation. In actuality, IMAP is the preferred method and that is what I now use on all my PCs, tablets, and smart phones. I leave the rest of the POP info below for those interested.

In the following examples let's assume Bob Smith's email address is: bob.smith@example.com


When using both a home machine and a laptop to access the same email account the user must manually manage the synchronization of mail messages to ensure that, at a minimum, there is one machine that has ALL of the messages on it.

Mozilla stores email messages in folders within the Mail/News program component. Those folders are actually plain-text files in Windows and stored in your profile mail folder.

For more info on profiles see:

An example of a Windows XP Mozilla profile folder location is (read as one unbroken line):

C:\Documents and Settings\[windowsuser]\Application Data\Mozilla\Profiles\[profilename]\xxxxxxxx.slt\

For Bob Smith his Windows XP Mozilla profile mail folder location might be:

C:\Documents and Settings\[windowsuser]\Application Data\Mozilla\Profiles\[profilename]\xxxxxxxx.slt\Mail\bob.smith\

When you install Mozilla it creates a default profile with a set of standard folders:

You can create your own folders in Mozilla. For each folder in Mozilla there is a Windows file with the exact same name. Additionally, for each mail folder there is an index file of the same name with a ".msf" file extension, e.g. Inbox.msf, Drafts.msf, etc. The actual mail messages are stored in the mail file, the one withOUT a file extension. Do not manually delete those types of files or you will be deleting mail messages and they may not be recoverable. You should also backup your entire profile on a regular basis (see http://edmullen.net/mozilla/moz_info_ed.php).

Using Mozilla Mail

In our example here, when someone sends Bob an email it is received and stored on the someplace.net POP mail server. It stays there until Mozilla retrieves it and deletes it.

The most common approach is to set Mozilla Mail's preferences to download and then delete messages in order to free up space on the server for new incoming messages. This is selectable in Mozilla's preferences (Edit - Mail & Newsgroups Account Settings).

With this setup and only using one PC there is no issue: you receive (download) mail into Mozilla. The messages are stored in the various folders you have created in Mozilla. They are deleted from the POP server.

Out of Sync

If you use two computers the dilemma is how to have a complete set of messages on both machines. If you get your mail on PC1 those messages won't be on PC2 (e.g., your laptop). As time goes by more mail is received for your account by the someplace.net mail server. If you then use PC2 to access your account you now have messages on both PCs that are not on the other: The two PCs are out of sync.

When using PC2 to access mail, if Mozilla is set up the same way as PC1, then all the messages will be downloaded and stored locally on the laptop and deleted from the POP server. On the laptop are any replies you made and any new messages you created and sent while using the laptop. But they are not on PC1. Your two machines' Mozilla Mail data are now really out of sync. So how do we deal with this dilemma?

One Possibility

One way is to set up the laptop to always leave messages on the POP server. If you do this you can then get those messages into your home PC and both of your machines' incoming mail will be in sync, assuming no new messages have come into the POP server since the last time the laptop retrieved messages. However, you won't have any of the laptop replies or newly-created messages available on PC1. This is obviously not acceptable.

You could forward those replies and original messages from the laptop to yourself, sign off, run Mozilla on PC1 and download them. But that's messy. The messages will have extraneous "stuff" in them due to the forwarding process.

Let's say you have 100 mail messages stored on the laptop in a folder called Family and that 25 of them are new messages received since you last checked mail on PC1. PC1 only has 75 messages in Family. How do you get those new 25 messages from Family on PC2 to Family on PC1?

You could simply copy the Windows Family file to PC1. It will overwrite the existing file. This is ok if you started with both PCs in-sync at the beginning of this example. But what if you're not certain that your two systems were really in sync before you got new mail on PC2?

On PC2 create a new Mozilla Mail folder called laptopSync. Highlight all the new messages in Family and copy them to this new folder (highlight the messages, right-click on any highlighted message, choose Copy To and select the laptopSync folder).

In Windows Explorer find the laptopSync file in your profile mail folder. With Mozilla not running on PC1, copy the file to the mail folder on PC1 using a floppy, CD, or network. Open Mozilla Mail. There will be a new Mozilla mail folder called laptopSync containing the 25 new messages. Simply copy them to the Family folder. Delete them from the laptopSync folder on both PCs. You should also copy any replies you made and new messages you composed on the laptop using this technique.

If the volume of messages on the laptop is relatively small this works fine. If, however, you have a lot of mail activity, you can create as many transfer sync folders/files as you need, e.g., laptopSyncFamily, laptopSyncFriends, laptopSyncBusiness, etc. This will make it easier to sort things out when transferring to PC1. Easier but not ideal.

Yet Another Wrinkle

If you travel frequently and use Firefox and Thunderbird as your browser and mail/news you might want to investigate John Haller's customizations of these programs. He's created special versions dubbed "Portable Firefox" and "Portable Thunderbird" (and some other apps) which will run on removable media such as a CDR-W, Zip drive, USB drive, etc. They've been very well received and downloaded well over a quarter of a million times.

If you use only the portable versions there is no issue with synchronization. If, however, you use both home-based and portable installs you still have to deal with the sync issues described on this page.

the preferred method

IMAP is what I've been using for years now and don't really have any POP accounts anymore. With IMAP simply set up your mail accounts the same way on each machine. In SeaMonkey mail go to Edit - Mail & Newsgroup Account Settings. In each account go to Synchronization & Storage. Put a check in the box for "Keep messages for this account on this computer. That way you'll have all your mail even when off-line. I also select "Synchronize all messages locally regardless of age" and do not limit the size of downloaded messages. I also do not select any automatic deletion of messages.

While in this menu click the Advanced button. Here you can select what folders you want to sync with the IMAP server. I select everything.

Here's an additional trick. My laptop and desktop systems are set up exactly the same in terms of drive letters, files and folders, and SeaMonkey profile names. Since my desktop is my main system to make sure my laptop profile is in sync in terms of bookmarks, address books, history, passwords, form fill-in info, etc., I periodically simply copy the destop profile over top of the laptop's profile. Voila! Instantly the two systems are identical. If while travelling I save some bookmarks, change/add some passwords etc. I can simply copy those files to the desktop machine when I get home.

This page last changed: Sunday, October 25, 2015 - 01:42 PM USA Eastern Time

Copyright Ed Mullen | Contact Ed

click for home page