If you don't have it then please get it from the specific OS repository or the link provided at the begining of this article.
I am sitting on Gentoo and I got it like below:
bhaskar@bhaskar-laptop_09:46:16_Wed Dec 15:~> sudo emerge -av mutt                                                                                                                
Password:                                                                                                                                                                         
These are the packages that would be merged, in order:                                                                                                                            
Calculating dependencies... done!                                                                                                                                                 
[ebuild   R   ] mail-client/mutt-1.5.20-r18  USE="berkdb crypt gdbm nls ssl -debug -doc* -gnutls* -gpg* -idn -imap* -mbox* -nntp -pop* -qdbm -sasl* -sidebar -smime* -smtp* -tokyocabinet" 0 kB                                                                                                                                                                     
Total: 1 package (1 reinstall), Size of downloads: 0 kB                                                                                                                           
Would you like to merge these packages? [Yes/No]                                                                                                                                  
So I already have it in my system so there is no point getting it again.Let me check out when I got this;
bhaskar@bhaskar-laptop_09:49:46_Wed Dec 15:~> sudo genlop -t mutt                                                                                                                 
* mail-client/mutt                                                                                                                                                               
Wed Nov 24 11:16:02 2010 >>> mail-client/mutt-1.5.20-r18                                                                                                                     
merge time: 10 minutes and 53 seconds. 
Anyway ,it deflates configuration files in /etc/mutt like below:
bhaskar@bhaskar-laptop_09:51:46_Wed Dec 15:/etc/mutt> ls
Muttrc  Muttrc.dist  mime.types  mime.types.dist
Now What I do;read few article on the internet about gmail integration with mutt(which I will provide the link in the resource section at the bottom of this post).Now I have copied the Muttrc file to my home dir and make adjustment to that file.
My personal .Muttrc look like below:
1 # Some minimal Mutt settings, Gentoo-style.  Since mutt was installed
2 # with USE=mbox, this file doesn't have any changes from the default
3 # mutt settings, making it very minimal indeed...
4 #
5 # Please don't add settings to this file to change other user
6 # preferences (such as colors), since those can be hard for a user to
7 # undo if their preference doesn't match yours!  For example, it is
8 # *impossible* currently in mutt to remove color settings from objects
9 # other than the index.
10 #
11 
12  set imap_user="unixbhaskar@gmail.com"
13  set imap_pass=""
14  set pager_context=1
15  set pager_index_lines=6                 #show a mini-index in pager
16  set menu_scroll
17  set pgp_verify_sig=no                   #dont show pgp in pager
18  set status_on_top                       #put status line at top
19  set sort=threads                        #sort by message threads in index
20 #
21  set status_format=" %r %b %f %n      Del %d      Msgs %m %l %> (%P)"
22  set pager_format="%-10.10i %[!%a %b %d %R]"
23  set date_format="!%H:%M %a %d %b     "
24  set index_format="%4C %Z %[%b%d] %-15.15F %s"
25  set folder_format="%2C %t %8s %d %N %f"
26 #
27 # #set sendmail="/usr/bin/nbsmtp -d isp.net -h smtp.isp.net -f yourname@isp.net"
28 #
29  set from="unixbhaskar@gmail.com"         #set to your from address
30  set realname="Bhaskar Chowdhury"
31 #
32 # set record="$home/sent"        #sent mail is saved here
33  set delete=yes                          #delete without prompting
34  set include=yes                         #quote msg in reply
35  set fast_reply=yes                      #no prompting on reply
36  set beep=no                             #no noise
37  set markers=no                          #no + on wrapped lines
38  set confirmappend=no                    #no prompt for save to =keep
39  set to_chars=" +TCF"                    #no L for mail_list
40 #
41  set folder = "imaps://imap.gmail.com:993"
42  set spoolfile = "+INBOX"
43  set postponed ="+[Gmail]/Drafts"
44 
45  set header_cache =~/.mutt/cache/headers
46  set message_cachedir =~/.mutt/cache/bodies
47  #mailboxes =inbox
48 # mailboxes =gentoo-dev
49 # mailboxes =gentoo-announce
50 # mailboxes =gentoo
51 # mailboxes =freshmeat
52 # mailboxes =duplicates
53 # mailboxes =default
54 # mailboxes =friends
55 # mailboxes =junk
56 # mailboxes =spam
57 # mailboxes =keep
58 #
59 set smtp_url = "smtp://unixbhaskar@smtp.gmail.com:587/"
60 set smtp_pass = ""
61 save-hook .* =keep                      #default mbox to (s)ave mail is =keep
62 # subscribe gentoo-user gentoo-dev        #subscribed to these lists
63 #
64 # bind pager h display-toggle-weed        #toggle headers with h key
65 #
66 # # simulate the old url menu
67  macro index \cb |urlview\n 'call urlview to extract URLs out of a message'
68  macro pager \cb |urlview\n 'call urlview to extract URLs out of a message'
69 #
70 # #run fetchmail by hitting key of G
71  macro index G "!fetchmail -a -m 'procmail -d %T'\r"
72  macro pager G "!fetchmail -a -m 'procmail -d %T'\r"
73 #
74 # #use to edit .muttrc and then source it...no restart necessary
75 # macro generic ,sm ":source $HOME/.muttrc\r"
76 # macro generic \cj "!rxvt -bg wheat -e joe $HOME/.muttrc\r"
77 #
78 # # default list of header fields to weed out when displaying mail
79 # #ignore them all and then unignore what you want to see
80 # ignore *
81  unignore  Date To From: Subject X-Mailer Organization User-Agent
82  hdr_order Date From To Subject X-Mailer User-Agent Organization
83 #
84 # ##your Mutt has to have some colors
85 # ##these are for four levels of quoted text
86 # ##they override the system settings in /etc/mutt/Muttrc
87 #
88 # #color quoted green  default
89  color quoted1 magenta blue
90 # #color quoted2 yellow default
91 # #color quoted3 red default
92 # #color signature cyan cyan
93 #
94 #
95 # #this color setup is copied from /etc/mutt/Muttrc.color
96 # #comment it out if you want the default colors in /etc/mutt/Muttrc
97 # # Je vois la vie en rose :-)
98  color   hdrdefault      brightcyan      blue
99  color   header          brightwhite     blue "^from:"
100  color   header          brightwhite     blue   "^subject:"
101 #
102  color   quoted          brightgreen     blue
103  color   signature       brightwhite     blue
104 #
105  color   indicator       blue            green
106 #
107  color   error           red             black
108  mono    error           bold
109  color   status          black cyan
110  mono    status          bold
111  color   tree            yellow          blue
112 #
113  color   tilde           brightmagenta   blue
114  color   body            brightwhite     blue    "[-a-z_0-9.]+@[-a-z_0-9.]+"
115   mono    body            bold                    "[-a-z_0-9.]+@[-a-z_0-9.]+"
116  color   body            brightyellow    black   "^Good signature"
117  mono    body            bold                    "^Good signature"
118  color   body            brightwhite     red     "^Bad signature from.*"
119  mono    body            bold                    "^Bad signature from.*"
120  color   normal          white           blue
121  color   message         green           black
122  color   attachment      brightgreen     blue
123 #
124 # # End of file...but it can go on and on and on....:)
125 #
So the next job is to invoke mutt from the commandline like below:
mutt
and here is the outcome of that..it's connecting to gmail..
Now look at the bottom of the picture it fetching the header of those messages(it doesn't download the whole message).Only when you select the message for viewing then only mutt download the whole message.Once it get the headers it shows off the inbox like below:
Once the the headers are fetched it display the mail boxes you have with Gmail.Then you need to choose the proper box to show off those mails reside in it.Now select the any inbox and press enter then:
Anyway you can also integrate GnuPG with it for encryption and signing.
Hope this will help.
Cheers!
Bhaskar
Resources:
1) http://www.andrews-corner.org/mutt.html
2) http://wiki.mutt.org/index.cgi?MuttGuide
3) http://crunchbanglinux.org/wiki/howto/howto_setup_mutt_with_gmail_imap
4) http://www.faqs.org/docs/Linux-HOWTO/Mutt-GnuPG-PGP-HOWTO.html


