Ensuring that email gets through

Posted on 2004-11-04
Last Modified: 2010-04-10
We have a program that has the capability of sending and receiving email.  Consider that many users are connecting through an ISP to the internet.  The problem that we sometimes encounter is that we are sending an email directly through to our SMTP server and the ISP does not like that, for obvious reasons.  I believe the process goes as follows:
1. user sends email to using
2.  traffic gets to ISP, ISP checks that the email is not using their SMTP server and sometimes drops this request

We do not want the user to bother with finding out their login info and ISP SMTP server address, that is not an option.  So far, we only have work arounds to this and would like to know what options we have to do this.  For instance, http traffic is never dropped so perhaps there is a way of carrying the email inside an http request.  One more thing to note is that webmail per se is not an option, there are/will be too many users so an apache/imap/webmail solution is not an option.
Any suggestions are welcome.  
Question by:bisonfur37
    LVL 8

    Accepted Solution

    When you say do you mean you actually have a mailserver which the program sends them to (i.e. exchange, sendmail) or does the program attempt to deliver the email directly to the recipient domain bypassing your ISP's smtp server altogether?
    LVL 10

    Assisted Solution

    Hi bisonfur37,
    Well, you can change the ports your server and the clients are using. This sounds like a very bothersome ISP.

    LVL 8

    Assisted Solution


    As kain21 points out, there is no general requirement that your mailserver relay mail through the ISP's mailserver. In fact, depending on the rules your ISP uses, that may be against policy.

    Some ISP's, such as AOL, implement their mail handling by proxying SMTP, which can cause some strangeness if you are not expecting it. In general, unless the terms of service explicitly state that you cannot use SMTP directly to the destination, there should be no need to use the ISP's server at all.

    I hope that the above is helpful.

    - Bob (aka RLGSC)
    LVL 15

    Assisted Solution

    I would agree with NetworkArchitek, but if your firewall/internet router does PNAT then you only need to change the port SMTP uses at the client end. Let's say you make it 8080, just port translate incoming connections to your mail server 8080 to 25.

    Featured Post

    How to run any project with ease

    Manage projects of all sizes how you want. Great for personal to-do lists, project milestones, team priorities and launch plans.
    - Combine task lists, docs, spreadsheets, and chat in one
    - View and edit from mobile/offline
    - Cut down on emails

    Join & Write a Comment

    What’s a web proxy server? A proxy server is a server that goes between clients and web servers, used in corporate to enforce corporate browsing policy and ensure security. Proxy servers are commonly used in three modes. A)    Forward proxy …
    Data center, now-a-days, is referred as the home of all the advanced technologies. In-fact, most of the businesses are now establishing their entire organizational structure around the IT capabilities.
    After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
    In this tutorial you'll learn about bandwidth monitoring with flows and packet sniffing with our network monitoring solution PRTG Network Monitor ( If you're interested in additional methods for monitoring bandwidt…

    746 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    17 Experts available now in Live!

    Get 1:1 Help Now