Thursday, December 28, 2006

Configuring fetchmail to work with gmail

Gmail uses the POP3-over-SSL protocol, which encrypts your messages, to pop your mails. Thus, we should get a legel certificate for verification. You can use any legal certificates, here we will grab Google's own cerificate and authenticate it.

  1. Get gmail's own cerificate:
    $ openssl s_client -connect smtp.gmail.com:995 -showcerts
    Which will output such below:
    CONNECTED(00000003)
    depth=0 /C=US/ST=California/L=Mountain View/O=Google Inc./CN=pop.gmail.com
    verify error:num=20:unable to get local issuer certificate
    verify return:1
    depth=0 /C=US/ST=California/L=Mountain View/O=Google Inc./CN=pop.gmail.com
    verify error:num=27:certificate not trusted
    verify return:1
    depth=0 /C=US/ST=California/L=Mountain View/O=Google Inc./CN=pop.gmail.com
    verify error:num=21:unable to verify the first certificate
    verify return:1
    ---
    Certificate chain
    0 s:/C=US/ST=California/L=Mountain View/O=Google Inc./CN=pop.gmail.com
      i:/C=US/O=Equifax/OU=Equifax Secure Certificate Authority
    -----BEGIN CERTIFICATE-----
    MIIC3TCCAkagAwIBAgIDBZIAMA0GCSqGSIb3DQEBBQUAME4xCzAJBgNVBAYTAlVT
    MRAwDgYDVQQKEwdFcXVpZmF4MS0wKwYDVQQLEyRFcXVpZmF4IFNlY3VyZSBDZXJ0
    aWZpY2F0ZSBBdXRob3JpdHkwHhcNMDUxMTE1MjEyMjQ0WhcNMDcxMTE2MjEyMjQ0
    WjBoMQswCQYDVQQGEwJVUzETMBEGA1UECBMKQ2FsaWZvcm5pYTEWMBQGA1UEBxMN
    TW91bnRhaW4gVmlldzEUMBIGA1UEChMLR29vZ2xlIEluYy4xFjAUBgNVBAMTDXBv
    cC5nbWFpbC5jb20wgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBAMP8LCYiLGJ/
    RihwcOi1V/zHVTw0Gfu+mI141Vjuuj2DtQoav8emwlXbu8gZoKP9GeMWpX1Vo9qN
    4gkslIToHmDnIwGjcaEAfpdhSR9g54Kf5Y7BEXVyco6mTIlpe9vsbV0dmB1FvLP2
    1N09dkUJfi7V0fjb8mcn3QYu6+6QNoxPAgMBAAGjga4wgaswDgYDVR0PAQH/BAQD
    AgTwMB0GA1UdDgQWBBTdASsopgao1m8hcEg0cDZhucltljA6BgNVHR8EMzAxMC+g
    LaArhilodHRwOi8vY3JsLmdlb3RydXN0LmNvbS9jcmxzL3NlY3VyZWNhLmNybDAf
    BgNVHSMEGDAWgBRI5mj5K9KylddH2CMgEE8zmJCf1DAdBgNVHSUEFjAUBggrBgEF
    BQcDAQYIKwYBBQUHAwIwDQYJKoZIhvcNAQEFBQADgYEAln3/pVqYnUXA1TVGzOqX
    LFhohGxpuNkr1UJnQmYxmZeB07uPBYRX8c0JXEKs29TmAHRsLhmp8kF36F11Dxgi
    Xm/Y8I9zgWHoMj7SL3Ve/u8K8K7XcUyUuaWmldLQAREafpFy+f+KYHGuAVh8hjy6
    XyPlMCqj+PNp8QXjgOcgO68=
    -----END CERTIFICATE-----
    ---
    Server certificate
    subject=/C=US/ST=California/L=Mountain View/O=Google Inc./CN=pop.gmail.com
    issuer=/C=US/O=Equifax/OU=Equifax Secure Certificate Authority
    ---
    No client certificate CA names sent
    ---
    SSL handshake has read 891 bytes and written 314 bytes
    ---
    New, TLSv1/SSLv3, Cipher is DES-CBC3-SHA
    Server public key is 1024 bit
    Compression: NONE
    Expansion: NONE
    SSL-Session:
       Protocol  : TLSv1
       Cipher    : DES-CBC3-SHA
       Session-ID: C376985C4DAFD52F21A89E42FB9D36DA0458F3A6F1D97E9615A0793DE2C2163C
       Session-ID-ctx:
       Master-Key: 74C5BE3ACBEE15367F1D7ADCD91B478B0FD81FC9EDB56D8698C1DCAEE09CAEECCE58C557308CBE0C049EFB50D1EB2829
       Key-Arg   : None
       Start Time: 1167236180
       Timeout   : 300 (sec)
       Verify return code: 21 (unable to verify the first certificate)
    ---
    +OK Gpop ready for requests from 210.77.27.77 f57pf402492pyh
    

    Then, the Gmail's certificate is just the content between -----BEGIN CERTIFICATE----- and -----END CERTIFICATE-----. Prepare a directory to save your certificates, for example, ~/.certs/. Copy such content and save into the file ~/.certs/gmail.pem

  2. Get the Fingerprint of the certificate, run the command below:
    $ openssl x509 -fingerprint -md5 -noout -in gmail.pem
    MD5 Fingerprint=59:51:61:89:CD:DD:B2:35:94:BB:44:97:A0:39:D5:B4
    

  3. Rehash the gmail certificates:
    $ c_rehash ~/.certs
    Doing /home/nini/.certs/
    gmail.pem => 7f549ca4.0
    

  4. Now, the configuration of POP3-over-SSL has mostly completed. Verfiy whether everthing is ok by the following commands:
    $ openssl s_client -connect pop.gmail.com:995 -CApath ~/.certs -quiet
    depth=1 /C=US/O=Equifax/OU=Equifax Secure Certificate Authority
    verify return:1
    depth=0 /C=US/ST=California/L=Mountain View/O=Google Inc./CN=pop.gmail.com
    verify return:1
    +OK Gpop x99xx9999xxx ready.
    CAPA
    +OK Capability list follows
    USER
    RESP-CODES
    EXPIRE 0
    LOGIN-DELAY 300
    X-GOOGLE-VERHOEVEN
    .
    USER username@gmail.com
    +OK send PASS
    PASS password
    +OK Welcome.
    CAPA
    +OK Capability list follows
    USER
    RESP-CODES
    PIPELINING
    EXPIRE 0
    LOGIN-DELAY 300
    TOP
    UIDL
    X-GOOGLE-VERHOEVEN
    .
    QUIT
    +OK Farewell.
    read:errno=0
    

  5. Then, configure your ~/.fetchmailrc file, here is a good example:
    poll pop.gmail.com with proto POP3 uidl
        username "username@gmail.com" there with password "password" is "nini" here
        options keep ssl sslfingerprint
        '59:51:61:89:CD:DD:B2:35:94:BB:44:97:A0:39:D5:B4'
        # sslcertck sslcertpath "/home/nini/.certs"
        mda "/usr/bin/procmail -d %T"
    

    If your fetchmail is not running as a deamon but a crontab task, use the configuration file above and make sure the line contained sslcertpath is commented. Otherwise, you might occour the error:

    fetchmail: Server certificate verification error: unable to get local issuer certificate
    25424:error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed:s3_clnt.c:894:
    fetchmail: SSL connection failed.
    

    Perhaps, this has exposed a slight difference in logging behaviour between daemon mode and single instance mode. you can test it with the command:

    $ fetchmail -d0 -v pop.gmail.com
    

Use esmtp over smtp server

  1. Edit the configuration file ~/.esmtprc:
    hostname = smtp.gmail.com
    username = "username@gmail.com"
    password = "password"
    starttls = enabled
    
  2. $ chmod 0710 ~/.esmtprc
  3. If you use mutt as your mail client, then modifiy ~/.muttrc
    ~/.muttrc

    set envelope_from set sendmail="/usr/bin/esmtp -v -X ~/.esmtplog" my_hdr From: "username@gmail.com" my_hdr Reply-To: "username@gmail.com" set sendmail_wait=0

Reference:

4 comments:

badzil said...

Had some problems with Gmail and certificates (""Server certificate verification error: unable to get local issuer certificate"). Your tutorial was the only one I found giving me a working solution.

Nice work !

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DD said...

Thanks for this, helped with the last bit of the puzzle. Didn't spot the # in front of sslcertk which caused a blip. Note for bsd users there is no c_rehash script, just do the symlink yourself with
-------------------------------------
ln -s gmail.pem \
`openssl x509 -hash -in gmail.pem -noout`.0
-------------------------------------
which in effect pastes the result of the hash function into the symlink. NOTE this ASSUMES that there are no existing hash symlinks so check ~/.certs/ first and if in doubt use an iterative script or insert the trailing .n by hand

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