smtp2s3

A container to receive SMTP messages and route them to S3 storage.

Configuration

The container is configured via environment variables.

• AWS_ACCESS_KEY_ID The public identifier for your AWS account used to specify which account is making a request.
• AWS_SECRET_ACCESS_KEY The private cryptographic key paired with the access key ID to securely sign and authenticate AWS API requests.
• DNSBL_ZONES A CSV separated list of Domain Name System blocklist zones (e.g. "zen.spamhaus.org") to test the session IP against.
• LOG_LEVEL The verbosity of the logging. Valid values are DEBUG, INFO, WARN (or WARNING), ERROR or CRITICAL. The default is WARN.
• S3_ENDPOINT_URL The endpoint to connect to the S3 service.
• S3_PREFIX_PATTERN A URL for the prefix of the path to the S3 object to be written. See below for more information.
• SMTP_DATA_SIZE_LIMIT The maximum size in bytes for a message to be accepted. Defaults to 10MB.
• SMTP_HOSTNAME The host name to run the SMTP service on. The default is 127.0.0.1.
• SMTP_PORT The port number to run the SMTP service on. The default is 8025.
• SMTP_RECIPIENT_REGEX a regex that recipient email addresses must match for the message to be accepted. Default is

  (?:[\u00A0-\uD7FF\uE000-\uFFFFa-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[\u00A0-\uD7FF\uE000-\uFFFFa-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[\u00A0-\uD7FF\uE000-\uFFFFa-z0-9](?:[\u00A0-\uD7FF\uE000-\uFFFF-a-z0-9-]*[\u00A0-\uD7FF\uE000-\uFFFFa-z0-9])?\.)+[\u00A0-\uD7FF\uE000-\uFFFFa-z0-9](?:[\u00A0-\uD7FF\uE000-\uFFFFa-z0-9-]*[\u00A0-\uD7FF\uE000-\uFFFFa-z0-9])?|\[(?:(?:(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9]))\.){3}\])
  

Substitution in the S3_PREFIX_PATTERN

The following substitutions will be made in the provided pattern to create the path for writing the data to:

• {YYYY} for the year.
• {MM} for the month (zero padded).
• {dd} for the day (zero padded).
• {HH} for the hour (zero padded).
• {mm} for the minute (zero padded).

For example if S3_PREFIX_PATTERN is set to:

s3://mybucket/emails/year={YYYY}/month={MM}/day={dd}/hour={HH}/minute={mm}

Then the data for messages will be written to an object with a name looking like:

s3://mybucket/emails/year=2025/month=08/day=12/hour=06/minute=38/b307edd6-6d17-44e2-9af3-3369227cd647.eml.gz

There will also be a separate file called:

s3://mybucket/emails/year=2025/month=08/day=12/hour=06/minute=38/b307edd6-6d17-44e2-9af3-3369227cd647.json

which contains metadata about the message sender and recipients.