Why is it that RoundCube is receiving emails randomly?

[clever1]

I
Finally got my email setup and getting received emails but the weird thing is that I am getting the received emails randomly. Sometimes I even think it is not working.
Is there a way to prioritize the emails recieved and getting it quickly?.
Will this work differently if I use like thunderbird or other email client?

[skurudo]

Try to check logs - /var/log/dovecot.log
Nope, mail client don't affect anything.