Totally agree with this.

It's like Mobile Commerce in the early 2000s. Yes, technically you could do online shopping over the wap protocol at kbps speeds on your minuscule monochrome display. But did people actually do it? No.

As a non-English speaker, I was actually happy to learn something new today. Thanks @devslash0

Microsoft has once again taken a technological leap and launched today a most-awaited feature that has been years in the making. The removal of double spaces!

You are not your body. Who you are was never born, and will never die. Realise that and you will see you question through a whole different angle. You can start with "I am That" by Sri Nisargadatta Maharaj.

... and I can safely write that there is no way you will ever achieve anything comparable to gmail.

You can try:
- squirrelmail, ugly and so last century
- openwebmail, old-fashioned Perl webmail, not maintained any longer
- zimbra mail, lots of functionalities and fancy features
- roundcube, decent but nowhere near what you're hoping for

Spam control on the server side is going to be an issue. You will have to use a combination of solutions (e.g. custom sendmail configs, RBL/XBL blacklists, spamassassin, greylisting, procmail rules, smf-spf, j-chkmail) and it will take quite some time and effort to get everything fine-tuned.

For anti-virus, clamav works well

For IMAP I found that dovecot does a decent job. If you want to fetch from remote servers into your own server then fetchmail can do the job.

Usual security considerations apply - patch early, patch often.

You will spend long hours maintaining this, highly recommend using a log colorizer to help watching logs e.g. ccze
In the end you will feel you got a half-baked solution that doesn't even come close to comparing to gmail in terms of functionality, ease of user interface, security and spam control. But hey, it'll be your own stuff.