Introduce a msg format "maildir" like in Thunderbird (in addition to mbox). Many advantages

I would appreciate if a new message storage format “maildir” could be introduced in emClient in addition to the default mbox format.

This format is similar to EML and represents one file per message. Thunderbird and other email clients supports it.

It offers various advantages over mbox:

(Differential) Backup is easier. When I create only one message my whole mbox (with > 2 GB file size) must be backupped every time. With m aildir only one tiny single file.

Furthermore locating, retrieving and deleting a specific message is MUCH faster than with mbox. 

See further informaton here:

or here:

Could you add this storage format to emClient as well?

Thank you



Hi Peter,
thank you for sharing your idea on the forum, I have changed it from Question type to Idea type so other users can vote for this idea if they want to support it.
I will add it to our feature request list so our developers can consider it for future versions of eM Client.


I strongly advocate for support of maildir format, because with a large number of emails maildir format is about the only way how to keep emails in sync between two sites. I am not using eM Client yet, only because of the lack of this feature (and I refrain from suggesting eM Client as a solution to the email-client and calendar mess our department is suffering from with its mostly Linux but also other OS users).

In these Corona times, I have my emails in a mail directory tree shared between work and home office via Nextcloud. Thus only new emails are synced, rather than single giant files (MBOX or whatever). The additional traffic necessary for giant files is not the only killer argument, though. The second problem is even worse, I think, and occurs if I use my email client at work and home concurrently (e.g. this happens, if I need to go to my work PC, because my home laptop is broken again). Concurrent changes on both sides are impossible to merge with 10.000 emails in a single file – even more so if the file format is not open (like for eM Client).

IMAP and Exchange do exactly that. They do not rely on whichever method the email client uses to cache offline data, or how it is stored within their database. The messages are stored on a server and accessible from any number of email clients (desktop and phone) without the need to sync data directories across sites.

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Right, but unfortunately the settings of both are usually not in the control of the end-user (which is – I guess the group of users using your software). For instance, I have no means of motivating our admins to provide me with the mailbox-size I’d need for my emails.

It may work if only recent emails are relevant, but I repeatedly have to search for emails that I received like a year or longer back.

So this is an issue with your email provider, rather than with eM Client. Maybe consider another provider, or even a second provider to act as an online archive. Most free email providers offer a fair mailbox size. is apparently unlimited though they do restrict sudden massive increases. Maybe don’t try and transfer more than 1GB into the archive per day.

Automatic Archiving is designed to reduce server usage, and store your older messages in Local Folders. If you are using eM Client on more than one device though, those archives would not sync between them.

Changing the “email-provider” means changing my job :smile: – it’s my employer and I am working in public/health sector with patient-data – so Google & Co. wouldn’t be good alternatives :thinking:.

But I see that using another strategy for managing my emails (such as archive folders per year or so) may alleviate the problem. I will try whether I can get a good workflow with eM Client. In any case, I just wanted to describe the situation. Thanks for listening and taking my use case serious, Gary!

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