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

I have found Mail to be much improved following Johann's recommendations.

What I would like to add is the first time I followed Johann's advice I overlooked that I needed to make these edits individually to each of my four (4) mailbox accounts.

If you have multiple accounts usually the first account is highlighted when you enter Preferences. After making edits to that account, be sure to click on each of your other accounts and verify what is checked or unchecked in all of your other accounts.

under the mailbox menu the last item is "rebuild." Do this for each mailbox. The mail will seem to disappear but when the rebuild is done, how long depending on how many messages are in the mailbox, everything should be back and mail.app should run faster.