occording to qmail , there isn't any competitor or just like or better than that,
but i think no one is perfect. any one knows about what are dis-advantages of qmail vs other smtp servers

They are right, there's nothing better then that. Two disadvantages that I could say is, sometimes, pop and smtp servers can not work under high traffic (I guess every service has the same problem under high traffic ). I also think that 1GB is a huge waste of resources. Period. Nobody really needs that amount of space for e-mail. They could offer some webspace instead...

I also like Novell's myrealbox, but it's no gmail when it comes down to web interface. Gmail is just great

Gmail has competitors, but no one can pwn them, or at least haven't for now

The original question was about qmail, not Gmail.

To be honest there isn't anything I've wanted to do with an smtp server that qmail couldn't do and it's really fast as well.

Oh, sorry, I wasn't paying attention.

The last company I worked for used qmail in which we were about to dump to use postfix instead.

Some of the reasons we saw and had to deal with qmail:

1. Couldn't handle massive amounts of incoming mail or outgoing mail. We were always constantly having to deal with email queue issues. We had clients that sent out email using one of our servers to their customers, basically spam in a slightly different kind of way, but anyways, qmail always fscked up during high loads.
2. It always seemed we had to add a patch or go thru a million jumps just to have some kind of functionality for qmai when postfix and many others already have the functionality without going thru so much trouble.
3. Always saw random issues with later versions of Outlook and other email clients people in our company used which I think was partly Outlook's problem but still, not a solution if your getting strange intermittant connections that are very hard to track down and fix when all the admins using Linux never saw any problems, logs indicated nothing most of the time.
4. When the diehard admin who setup the qmail servers turns his back cause he's tired of dealing with it, you know its not worth your time or trouble.
5. The maintainer is full of himself and an arsehole..

My opinion when you should use qmail:

1. Got a lot of time configuring it how you want it to work.
2. Small business or very small mail server with a small load.

Sincerely,

An admin who no longer has to deal with qmail and truly doesn't like it.

PS. I wasn't that diehard admin who turned against qmail, I've always hated qmail cause I first learned sendmail and then found postfix to be the more stable, more secure, easy to configure and updated more often sendmail..

Don't you worry. That makes two of us . I'm sorry too...

thanks to all for reply.