Identifying and deleting large emails

[#1]

I regularly get the message to reduce the size of my mailbox.   There are a few separate mailboxes within my overall mailbox, each associated with a different email address within my username.  One of those mailboxes has 6000+ emails in because, for that box, POP3 isn't an option as the mails the box need to be accessed from multiple devices.

I want to reduce the size of that particular mailbox ideally by sorting it into descending message size (some will have large attachments) and considering which of those emails to delete first.   But there's no way to do this.  Frustratingly, it's not even possible to see which messages are the largest ones even without the sort.

Is there no way at all of seeing which messages are the large ones? 

[#2]

I use Magic Mail monitor programme, but am a POP3 user.
Could you temporarily convert to POP3, use Magic Mail Monitor to do what you need,
then, go back to IMAP settings?
https://sourceforge.net/projects/mmm3/

One other thought, can you not do anything using your webmail?

[#3]

Thanks but converting to POP3 or temporarily using a POP3 client will remove the emails from the server so isn't a solution.   I need to keep the emails that I want to retain, on the server.

[#4 · Accepted solution]

Why is sort by size not possible for you?  The majority of email clients facilitate this ... though you might need to add SIZE to the displayed columns.