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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for the ‘SMTP’ Category

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On my list of things to try: Amazon SES for outbound/inbound email handling

Posted by jpluimers on 2021/08/10

SES mail servers at the time of writing

*n*x:

# nslookup -type=TXT amazonses.com | grep "v=spf1"
amazonses.com   text = "v=spf1 ip4:199.255.192.0/22 ip4:199.127.232.0/22 ip4:54.240.0.0/18 ip4:69.169.224.0/20 ip4:76.223.180.0/23 ip4:76.223.188.0/24 ip4:76.223.189.0/24 ip4:76.223.190.0/24 -all"I

Windows

C:\>nslookup -type=TXT amazonses.com | find "v=spf1"
Non-authoritative answer:
        "v=spf1 ip4:199.255.192.0/22 ip4:199.127.232.0/22 ip4:54.240.0.0/18 ip4:69.169.224.0/20 ip4:76.223.180.0/23 ip4:76.223.188.0/24 ip4:76.223.189.0/24 ip4:76.223.190.0/24 -all"

These addresses use a compact CIDR notation to denote ranges of networks containing ranges of network IPv4 addresses.

CIRD processing to sendmail access file

(this is linux sendmail only)

Converting the nslookup outout to a CIDR based sendmail /etc/mail/access excerpt goes via a pipe sequence of multiple sed commands:

# nslookup -type=TXT amazonses.com | grep "v=spf1" | sed 's/\(^.*"v=spf1 ip4:\| -all"$\)//g' | sed 's/\ ip4:/\n/g' | xargs -I {} sh -c "prips {} | sed 's/$/\tRELAY/g'"
199.255.192.0   RELAY
199.255.192.1   RELAY
...
76.223.190.254  RELAY
76.223.190.255  RELAY

What happens here is this:

  1. Filter out only spf1 records using grep.
  2. Remove the head (.*v=spf1 ip4:) and tail ( -all") of the output, see [WayBack] use of alternation “|” in sed’s regex – Super User.
  3. Replaces all ip4: with newlines (so the output get split over multiple lines), see [WayBack] linux – splitting single line into multiple line in numbering format using awk – Stack Overflow.
  4. Convert the CIDR notation to individual IP addresses (as sendmail cannot handle CIDR),
    1. This uses a combination of xargs with the  sh trick to split the CIDR list into separate arguments, and prips (which prints the IP addresses for a CIDR); see:
    2. Alternatively, use
  5. Replaces all end-of-line anchor ($) with a tab followed by RELAY, see

You can append the output of this command to /etc/mail/access, then re-generate /etc/mail/access.db and restart sendmail; see for instance [WayBack] sendmail access.db by example | LinuxWebLog.com.

Without the xargs, the output would look like this:

# nslookup -type=TXT amazonses.com | grep "v=spf1" | sed 's/\(^.*"v=spf1 ip4:\| -all"$\)//g' | sed 's/\ ip4:/\n/g'
199.255.192.0/22
199.127.232.0/22
54.240.0.0/18
69.169.224.0/20
76.223.180.0/23
76.223.188.0/24
76.223.189.0/24
76.223.190.0/24

Via

–jeroen

Posted in *nix, *nix-tools, Amazon SES, Amazon.com/.de/.fr/.uk/..., Cloud, Communications Development, Development, Infrastructure, Internet protocol suite, Power User, sendmail, SMTP, Software Development | Leave a Comment »

email file decoding: Encode/Decode Quoted Printable – Webatic

Posted by jpluimers on 2021/03/26

For my link archive: [WayBack] Encode/Decode Quoted Printable – Webatic.

It did a splendid job at decoding email files in MIME format Quoted-printable.

–jeroen

Posted in *nix, *nix-tools, Communications Development, Development, eMail, Encoding, Internet, Internet protocol suite, Power User, sendmail, SMTP, SocialMedia, Software Development | Leave a Comment »

Postfix TLS Support

Posted by jpluimers on 2021/02/25

For my link archive:

–jeroen

Posted in *nix, *nix-tools, Communications Development, Development, Internet protocol suite, postfix, Power User, SMTP | Leave a Comment »

Indy10, TIdSMTP, how to get protocol log?

Posted by jpluimers on 2020/12/17

Indy is great, but not well documented so: [WayBack] Indy10, TIdSMTP, how to get protocol log? I try to get log from SMTP communication, like this (copy from wiki): {code} S: 220 smtp.example.com ESMTP P… – Jacek Laskowski – Google+

Q

Indy10, TIdSMTP, how to get protocol log?

I try to get log from SMTP communication, like this (copy from wiki):

{code}
S: 220 smtp.example.com ESMTP Postfix
C: HELO relay.example.com
S: 250 smtp.example.com, I am glad to meet you
C: MAIL FROM:<bob@example.com>
S: 250 Ok
C: RCPT TO:<alice@example.com>
S: 250 Ok
C: RCPT TO:<theboss@example.com>
S: 250 Ok
C: DATA
S: 354 End data with <CR><LF>.<CR><LF>
C: From: "Bob Example" <bob@example.com>
C: To: Alice Example <alice@example.com>
C: Cc: theboss@example.com
C: Date: Tue, 15 January 2008 16:02:43 -0500
C: Subject: Test message
{code}

but without success :-(

I try use many events from TIdSMTP, TIdLogEvent, TIdSSLIOHandlerSocketOpenSSL but result is low level like bytes, status etc. not true SMTP log.

How to do it?

A

Sending stuff still might be tough, so you might want to consider alternatives too: [WayBack] I need to add to the REST server the ability to send emails with attachments of different types. Which library is best to use? Indy or maybe ICS? Of cou… – Jacek Laskowski – Google+

Q

I need to add to the REST server the ability to send emails with attachments of different types. Which library is best to use? Indy or maybe ICS? Of course with SSL/TLS support.

A

Dany Marmur's profile photo

Dany Marmur+2
+Balázs Szakály, YES! Synapse. Let’s get people using it more. You can give it some criticism surely, but consider the pro’s:

It is straight-forwardly-written so when you hit a wall you can read the code easily (compared to other solutions),

You can inherit, extend and extrapolate, re-use and tweak,

Very Delphi-ish (TMimeMessages = TStringList or some such, not at at devmachine atm)

Compact and free!

Quite stable too.

–jeroen

Posted in Communications Development, Delphi, Development, Indy, Internet protocol suite, SMTP, Software Development | Leave a Comment »

Some postfix notes

Posted by jpluimers on 2020/10/15

Postfix has documentation on primary MX and secondary MX, but not on tertiary MX.

If the primary MX is down, you have a series of secondary MX and tertiary MX that configured the same way, MX DNS priority for primary, the series of secondary MX and tertiary MX have increasing numbers, and the primary MX goes down, then senders can get “too many hops” as secondary and tertiary MX are looping.

I had a hard time finding a good and easy solution as these queries do not return many meaningful results:

Here are some links that helped getting this solved:

  • [WayBack] Postfix Frequently Asked Questions: What does “Error: too many hops” mean?

    Short answer: this message means that mail is probably looping. If you see this after you turned on Postfix content filtering, then you have made a mistake that causes mail to be filtered repeatedly. This is cured by appropriate use of content_filter=, header_checks=, and body_checks=.

    Long answer: the message has too many Received: message headers. A received header is added whenever Postfix (or any MTA) receives a message. A large number of Received: message headers is an indication that mail is looping around.

    Side comment: email uses the opposite of the technique that is used to avoid IP forwarding loops. With IP, the sender sets a TTL (time to live) field in the IP header. The field is decremented by each router. When the TTL reaches zero the packet is discarded and an ICMP error message is returned to the sender.

  • [WayBack] Error: too many hops (in reply to end of DATA command) · Issue #713 · mail-in-a-box/mailinabox · GitHub

    In case you or anyone else was/is wondering about the mydestination = localhost thing, the reason it has to be set to just localhost is because MIAB uses Postfix’s “virtual domain hosting” (http://www.postfix.org/VIRTUAL_README.html) support. Per the documentation for mydestination at http://www.postfix.org/postconf.5.html#mydestination:

    Do not specify the names of virtual domains – those domains are specified elsewhere. See VIRTUAL_README for more information.

    (in the context of MIAB every domain is a virtual domain).

In my case a series of these:

Received: from mwgp.xs4all.nl (mwgp.xs4all.nl [80.101.239.92])
    by fiber24315337242.heldenvannu.net (Postfix) with ESMTP id 26395200FE
    for <jeroen@pluimers.com>; Fri, 29 Jun 2018 11:01:02 +0200 (CEST)
Received: from fiber24315337242.heldenvannu.net (unknown [37.153.243.246])
    by mwgp.xs4all.nl (Postfix) with ESMTP id 077A5E937
    for <jeroen@pluimers.com>; Fri, 29 Jun 2018 11:01:02 +0200 (CEST)

Specifying the transport will likely help me solve this problem:

This all came down to editing /etc/postfix/transport adding lines for each relayed domain like this one:

example.org    smtp:[mx-a-record.example.org]

Lines like it direct to use the smtp transport and use a specific host (normally, the relay transport is being used).

After this:

# postmap /etc/postfix/transport
# rcpostfix reload

I choose not to configure [WayBack] Postfix Configuration Parameters: relay_recipient_maps, but might if I had an automated way of replicating lists of valid (and invalid) users.

Another option was confirmed at [WayBack] Software-update: Postfix 3.4.0 / 3.3.3 / 3.2.8 / 3.1.11 / 3.0.15 – Computer – Downloads – Tweakers by [WayBack] menocchio. Thanks!

Dat is volgens mij eenvoudig op te lossen met relay_transport of transport_maps. Zie ook: Postfix transport table format.

Daarmee dwing je de secondary servers de mail altijd af te willen leveren bij de primary server (en dus niet bij een andere secondary). En als de primary niet online is, dan wacht ie netjes tot dat wel het geval is :-)

Bijvoorbeeld:
relay_transport = smtp:[primarymx.domain.tld]

Likely relevant: [WayBack] The Book of Postfix

Maybe relevant in the future:

Found on my hunt for the above:

Try not to make typo’s: [WayBack] postfix appears not finding MX records or host names from DNS

Interesting thought, but not sure how smart SPAM bots are now: [Archive.is] Spam relaying through secondary MX… – Google Groups

To archive this:

  1. Rename from
  2. To
  3. Then save in Archive.is

–jeroen

Posted in Communications Development, Development, DevOps, DNS, Infrastructure, Internet, Internet protocol suite, Power User, SMTP | Leave a Comment »

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