Mac Mail has very slow to send/receive mail (plus other bugs too) It's been worse since Yosemite.

From the same exchange account (office365) I will send and receive emails instantly on my phone, but they will take several minutes through the app.

Loading existing conversations also often takes a long time.

Conversations often get jumbled up and emails that don't belong will be added to a conversation.

And finally accepting event invitations is a little messed up. I click accept and nothing happens. Then a few minutes later the email will dissapear and the event will appear in the calendar.

I am having these issues on both my laptops.

I've tried offlining and enabling the account. Also tried reindexing.

Does anyone know if these are just Yosemite bugs? Or is there somethinng I can do to fix it? 

Thanks!
I also had extremely slow mail using Yosemite until I did this:

From the Mail menu, click Preferences > Accounts > Mailbox Behaviors

Drafts:

Store draft messages on the server > leave unchecked

Sent:

Store sent messages on the server > leave unchecked

Junk:

Store junk messages on the server > checked
Delete junk messages when > Never

Trash:

Move deleted messages to the Trash mailbox > leave unchecked
Store deleted messages on the server > leave unchecked