docker-smtp-relay

Our adaptation of boky/postfix

What differs ?

We need to set ddns with a cloudflare record.
Note that you need an existing record before running. We need to provide a unique RSA dkim private key for all our domains.
At start a script will generate a dkim key for each ALLOWED_SENDER_DOMAINS , the selector will be mail or if DKIM_SELECTOR is the selector will be those in this environment variable.

For generating the there is many solutions ex:

openssl genrsa -out /dev/stdout 2048 | tr '\n' '|' | sed 's/.$//'

and store in in DKIM_PRIVATE_KEY

CLOUDFLARE_API_KEY="YCUENIMPORh8Lx0g72d"  \
CLOUDFLARE_ZONE_ID="554d………………c400fc" \
CLOUDFLARE_DNS_RECORDS="smtpd.example.org, smtpd2.example.org" \
ALLOWED_SENDER_DOMAINS="example.org example.com example.net" \
DKIM_PRIVATE_KEY="-----BEGIN PRIVATE KEY-----|MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDLkJAAw7tffhHu|yXW5kfN1IBvbfrFV9ZyavzrMMeh/WhZ4T7zto5x3n1KsTtHdYYV5f7O4i92QrXev|mCQjzawOI2o2OQ0uNSe7M8/ySYmyz8LvfLcA1/vRKluJ/+0WKvr2Rz5VkjTeH3qv|mJGjrFNvwkjzYPw1nzy+Vd9u/RLO0MHToLvCr9cOByJi4w9sj/nbusi83dEwfkW0|qiypWgbCK9ylLJfhJvV/kXlBFIjHog8WMJ6VLWF1SFCUB1wU2PBi1mwQX8rS18et|Td+qf+eDoMWFrHYsfTSVq8K6ZruarEpW87AmLT5ueYf6UpWFZyiuaNMHwSOXwQdE|F9Omiwl5AgMBAAECggEATHp9f6wJw3Cr8BiEQDnTS9fKX4aTvYXPVlwuDPVbMi14|b68VffqQGGklOFNMiW3QJbuSm+0ASxDA/JmeSk1FLPKlPsXka83QpYZrw81ZDHL9|+9fRMWHz27ucNJaQTlnLe6d8hc2uSx1sjHg3j1R47G4D1lxDpSm0OpYsoZg27rfX|qpjjfMfJCYP0cd+qGdS3Rkfo+R8FAlZFW9jUWkfIpJrshSGR/EJ8lthS1Jt3iCyt|85QKMKPC79x1AP3H5CsnVJ3xieLsKuECEcdfH76ISryNES/gelD/d8Tlz9stpA+V|RRWIvGIqxXWRAqTAdo/dD7douDOd/FQP2JfQ89xk2QKBgQDxslckA/XONe+prl0s|nZKY4jZ4jp0cSxQ2FoYLYVLRBTJ5CJDdpfRwVgyT+86qqyA/tIDee4uTIHSMMVT7|j8dGq3u3PGwjBo1c2SpAdUHNKYxSt06UNKvqWZtmIOfGPv5cudMaQJbKBhE/Xw2L|W5ctSHOT/EchQvobcWLX1OntlwKBgQDXnIe5v1EGUIB2gLPCOpz25FtLKJNyPGeh|l+FLcN3xtzKlLQucT1JJAspaMBni0Ir6pu6X8GWxmO9qKhDA8arW/PCh6CNrbxPy|Zmmwj0k070qz/9OqbJVngVOIMphKj4x6GAjhvCKThSmauLI9ja9BatxPKh/CaOJ+|JYOKDlXDbwKBgQCSgdZMoJHpc8xZALa+Cq4IOmdmYJxfwCr6NmD+mPoIdawIreaS|VLx9M8vgEC1QSvb7ZsEPG7iZcHz1Vhn7e0YCUoRlqByshpY+B+2SsQE4Cc1jfnYF|ZIApSDPojl2wUBMDxihuq2Q8Bb2Cum2NYfGbo2Vb+Pps8RqGdA7EYe2C9QKBgHBb|eb8qG6cWvFsEpqhIsxNV3N1Fv9B/+eETrKwLnR0hQpsg5jQGgfLaKWjmOBciZcpI|w30aIWRzNhA065YgWc6+8QbuWcbak6J2DA2eHaAgMuWqIztkalcN5eHLu+De/W2C|qN45lCsb8ZpXNUsuUm3cqgH3CaXd0mm6UtnWroqxAoGAY4FK7yt4Y+Y6MVx3kKUO|rxSPI0KqL9mH2JyWFexZziV3RuE7DIf+IFVPLsrxSrfsZqYOFuBamfPVLVHNx+Ma|dbDPH+KzOc5sMNDkLebWg+qddpTm6Zy0mUACRbFijF1TjPRiwnpEpScGUSS+Cs8U|Coe+cQBuoTsIHpowYjVbps4=|-----END PRIVATE KEY-----"\
DKIM_SELECTOR="hcfmailer" \
docker run -e DKIM_PRIVATE_KEY -e highcanfly/smtp-relay:latest

later in the log you will see the DNS proposal record.

hcfmailer._domainkey IN      TXT     ( "v=DKIM1; h=sha256; k=rsa; s=email; "        "p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAy5CQAMO7X34R7sl1uZHzdSAb236xVfWcmr86zDHof1oWeE+87aOcd59SrE7R3WGFeX+zuIvdkK13r5gkI82sDiNqNjkNLjUnuzPP8kmJss/C73y3ANf70Spbif/tFir69kc+VZI03h96r5iRo6xTb8JI82D8NZ88vlXfbv0SztDB06C7wq/XDgciYuMPbI/527rIvN3RMH5FtK"
       "osqVoGwivcpSyX4Sb1f5F5QRSIx6IPFjCelS1hdUhQlAdcFNjwYtZsEF/K0tfHrU3fqn/ng6DFhax2LH00lavCuma7mqxKVvOwJi0+bnmH+lKVhWcormjTB8Ejl8EHRBfTposJeQIDAQAB" )  ; ----- DKIM key mail for example.org

If you want to compute the TXT value locally, having DKIM_PRIVATE_KEY correctly setted:

echo $DKIM_PRIVATE_KEY | tr '|' '\n' | openssl rsa -pubout 2> /dev/null | sed -e '1d' -e '$d' | tr -d '\n' | echo "v=DKIM1; h=sha256; k=rsa; s=email; p=$(</dev/stdin)"

deploy

Get image at highcanfly/smtp-relay:latest

docker pull highcanfly/smtp-relay:latest

configuration

see bokysan/docker-postfix repository