Outgoing SMTP Servers

Posted on 2012-08-12
Last Modified: 2013-11-22
I am planning to setup SMTP server only for the outgoing mails.
I dont want to publish MX record for this.
What will happen if MX record is not configured. Will the receiving SMTP server will detect the mails from my SMTP server as SPAM.

What is the standard practice to setup the external SMTP server only for the outgoing mails.
Question by:SrikantRajeev
    LVL 82

    Expert Comment

    by:Dave Baldwin
    There is no standard practice for doing that and nobody else wants you to do that.  If you do this, you will look just like the spammers who send email from their home computer thru the SMTP server included with IIS.  You will almost certainly be regarded as spam because without an MX record, the receiving servers can not validate your email address or that you have a right to send email from that IP address.  The big web mail hosts like Gmail, Yahoo, and Hotmail are more interested in blocking spam than delivering email because they get 4 times as much spam as valid emails.
    LVL 11

    Expert Comment

    What Dave said here is of course right.

    If you really don't want to use your SMTP with incoming mail you can set it up to route all outgoing mail to your "other" (incoming) mail server (which hopefully has a correct MX record). I would not send mail from any server without an MX record because of the problems mentioned by Dave here.
    LVL 1

    Author Comment

    I will have 2 servers. 1 server I will use for incoming & the other server i will use for outgoing.
    For incoming mail server i will have the MX record. For the outgoing mail server i will not have MX record but i will have the SPF record configured.

    Let me know if this will be fine or still i need to have the MX record for my outgoing mail server also.

    Expert Comment

    MX record should not be required.  I would make sure to have a pointer record (PTR) setup with reverse record resolution to allow any receiving SMTP server to reverse lookup your sending server.  If the registered dns name of your server does not match the lookup IP, the receiving end may see it as SPAM.

    This is my first post, hope it helps.
    LVL 4

    Expert Comment

    Let me point out that @DaveBaldwin check is not listed on Wikipedia as a SPAM check but this does not means that some anti-spam software will take this verification as a partial sign of SPAM adding points to the SPAM score.
    If where you I would read carefully the Wikipedia reference and a will try to accomplish with everything listed.
    One of the most important ways to detect SPAM is by blacklist subscription, this lists will have a record for each ip with a SPAM incident detected so if you share with others the IP or if you share with others the mail server your email sent can be treated as SPAM just because one of your “partners” that you don’t even know is doing mail actions considered SPAM.
    SPF is not definitive in SPAM detection because many companies don’t have it, other have it wrong (I have receive one for a very famous credit card company that SPF fail but the email was legal), and spammers can make subdomains to keep parent free sending email from child with SPF records well register. Many company uses domains like:,, … so it is hard to detect for a anti-spam software which parent is fake and which one is legal.
    The important thing is that there is no way to tell for sure if is SPAM or not, so anti-spam software uses its score to make the decision.
    LVL 1

    Author Comment

    also if i dont have MX record  what will happen to the bounced back e-mail.
    If there is no MX record I will not come to know the details regarding my bounced back e-mail details.
    LVL 4

    Accepted Solution

    When the person who receive the mail press replay, the mail program will check “replay” and “from” fields of the message to fill the “to” field of the new one. Once the new email arrive to the outbound mail server the ‘to’ field spread in two parts, the mail sever will use the destination domain part to request to its DNS server for MX records of this domain. Now outbound sever will connect to destination inbound server to send the message. That is why outbound servers may not be inbound servers.
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