email with long thread jump size & take a long time to open

[satyas]

Hello everyone

We use outlook and thunderbird mail client (mostly thunderbird),
sometimes there is always a problem when try to opening email in outlook( email with long thread) that sent from thunderbird.
and sometimes email size jumping (we receive email form customer 500Kb then user with thunderbird mail client replying this email (only insert a few character and without picture), suddenly email size getting jumping almost 3Mb.
and when this email open with outlook mail client it take a loooong time to open.

we already digging about mail encoding, and understanding that email size will growing up, we try many addon but we still can't found solution why email take a long time to open in outlook (we already try in safemode, disable addinn and others), but nothing change.

can someone explain this and how is the solution so email can be open normally in outlook ?
(ps : email normal when open in client with thunderbird

thanks..