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Re: SMTP proxy?

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  • Daniel Bromberg
    ... Speaking not as a Postfix expert but as a DBA, and speaking more on administrative strategy rather than technically, I would consider merging the two
    Message 1 of 12 , Feb 1 10:38 AM
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      On 2/1/2011 12:50 PM, Ignacio Garcia wrote:
      >> You are not thinking very clearly yet. You must distinguish clearly
      >> between:
      >>
      >> - Submission, users submitting mail for outgoing delivery. This is
      >> visible to users, since they set the server in question as their
      >> MUAs "SMTP server". This needs its own design, and it is what I
      >> thought you wanted help with.
      >>
      >> - Inbound MX service. Just publish appropriate MX records, and add
      >> front-end SMTP servers to each of the two environments as necessary.
      >> In ISP-grade implementations the SMTP inbound servers are not also
      >> IMAP servers, rather they forward mail to IMAP servers (via LMTP
      >> or SMTP).
      >>
      >> Which do you need help with? State clear requirements for either or
      >> each problem, and work from there.
      >
      > yes, you're right, sorry. Maybe if I tell you what I want to do I can
      > make myself clearer. We have both a submission service and inbound mx
      > service. we want to have a unified smtp.mycompany.com so all
      > "submissions" can be processed using this canonical domain name. i
      > believe that is not too dificult. We also want to run both servers so 1
      > is mx-backup of the other and viceversa. However, I forsee several
      > problems here:
      >
      > - both servers need to check against both databases for valid
      > destinations
      > - each server must know if delivery is to be local or it has to be
      > relayed to the other server.
      > - one server virtual_transport=maildrop (to courier-imap), the other
      > =dovecot (we are going with dovecot for the future, the one with courier
      > is older, but plenty of users)
      >
      > So, is there any hope?
      >
      > Ignacio
      Speaking not as a Postfix expert but as a DBA, and speaking more on
      administrative strategy rather than technically, I would consider
      merging the two databases. This is just a guess that the two servers are
      running under the same organizational umbrella and that the DB's serve a
      similar purpose for a single organization. Ugliness will grow and grow
      around accommodating two databases that should be one.

      The unified DB would have a "server_a_user_table" and a
      "server_b_user_table" ([much] better yet, a unified table with a server
      tag column so arbitrary servers can be added ultimately). Then you have
      the flexibility to distinguish a local user lookup versus a relay lookup
      on each server by configuring each of transport queries appropriately.
      (Hint:
      http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html#function_if)

      Do the painful merging steps now and grow a sensible architecture that
      can last for years. All kinds of dust will get rooted out in the
      process. Optimistically your business will only need to add servers. An
      obvious initial benefit is the simplified backup and monitoring
      requirements.

      Then as others have mentioned, the MySQL architecture can be replicated,
      tuned, and accessed remotely with appropriate security settings. It can
      even be replicated while live by setting it to read-only during initial
      replication.

      I believe efficiency in a replicated setting will still be very high.
      Mail is very heavily read-oriented for DB's: settings/user migration/new
      users don't change that much but there are 10^n lookups a day.

      -Daniel
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