action timeout

hi everyone!

although i think i have a fairly common problem - i could not find a
solution via google right away.

basically i have an action sending out emails that has to run quite
long while being accessed throught a browser. about 30 minutes is
normal in this case.

right now i get a timeout error after 10 minutes and i don't know
which setting this is coming from.

this is what i have in my production.log:

ActiveRecord::Transactions::TransactionError (Transaction aborted):
    /var/lib/gems/1.8/gems/activerecord-2.0.2/lib/active_record/
transactions.rb:76:in `transaction'
    /usr/lib/ruby/1.8/net/protocol.rb:133:in `call'
    /usr/lib/ruby/1.8/net/protocol.rb:133:in `sysread'
    /usr/lib/ruby/1.8/net/protocol.rb:133:in `rbuf_fill'
    /usr/lib/ruby/1.8/timeout.rb:56:in `timeout'
    /usr/lib/ruby/1.8/timeout.rb:76:in `timeout'
    /usr/lib/ruby/1.8/net/protocol.rb:132:in `rbuf_fill'
    /usr/lib/ruby/1.8/net/protocol.rb:116:in `readuntil'
    /usr/lib/ruby/1.8/net/protocol.rb:126:in `readline'
    /usr/lib/ruby/1.8/net/smtp.rb:664:in `recv_response'
    /usr/lib/ruby/1.8/net/smtp.rb:396:in `do_start'
    /usr/lib/ruby/1.8/net/smtp.rb:686:in `critical'
    /usr/lib/ruby/1.8/net/smtp.rb:396:in `do_start'
    /usr/lib/ruby/1.8/net/smtp.rb:378:in `start'
    /usr/lib/ruby/1.8/net/smtp.rb:316:in `start'
    /var/lib/gems/1.8/gems/actionmailer-2.0.2/lib/action_mailer/
base.rb:586:in `perform_delivery_smtp'

[...]

where can i set this "max_exec_time" ??

thanks in advance and have a nice day
_f