A lot of different tools are around the internet which can be useful to determine different SMTP troubles.
The most of them are very useful but they are all reachable over the internet and don’t provide any kind of API for integration of monitoring or complex integration in (pre)deployment pipelines.
This is a short overview of some command line tools for developers and administrators, to check the e-mail flow during developing, emulate and intercept outgoing emails and afterwards for maintaining the setups.
swaks -s 127.0.0.1 -p 2025 -t email@example.com
Native python smtpd-library which is accessible from each python installation. smtpd-library starts a development smtp-proxy
python3 -m smtpd -n -c DebuggingServer -d 127.0.0.1:2025
For more debugging output, can be use the -d flag which Turn on the debugging prints.
dsmtpd is a small python-tool to help the developer without a running smtp server to debug the email flows, which gets generated from the code.
Installation works for any platform with python support:
pip3 install dsmtpd
Start dsmtpd on port 2025 and bind to localhost.
dsmtpd -p 2025 -i 127.0.0.1