Send Email With Python

This repository is for practicing sending email with python.

Requirements

• Python 3 (only the standard library is used — nothing to install)
• A Gmail account with 2-Step Verification enabled and an app password generated for it

Configuration

Three environment variables are read at startup. If any are missing, empty, or only whitespace, the program names every one of them and exits with status 1 before any connection is attempted. Leading and trailing whitespace (such as a stray space or a \r from a file saved with Windows line endings) is stripped from each value before it is used; spaces inside a value are kept.

Variable	Description
EMAIL_SENDER_ADDRESS	The Gmail address the message is sent from
EMAIL_SENDER_APP_PASSWORD	The 16-character app password for that account — not the account password
EMAIL_RECIPIENT	The address the message is sent to

export EMAIL_SENDER_ADDRESS="you@gmail.com"
export EMAIL_SENDER_APP_PASSWORD="abcdefghijklmnop"
export EMAIL_RECIPIENT="someone@example.com"

Usage

./run.sh

run.sh finds src/main.py relative to its own location, so it can be run from any directory (e.g. path/to/send-email-with-python/run.sh).

Or without the wrapper script, from the repository root:

python3 src/main.py

Either way the following prompt appears:

Use SSL or TLS? (s/t): 

The answer is case-insensitive and surrounding whitespace is ignored, so S or t work too.

• s — connects to smtp.gmail.com:465 over SSL
• t — connects to smtp.gmail.com:587 and upgrades the connection with STARTTLS
• Anything else — prints Invalid input! Please type 's' or 't'. and exits with status 1 without connecting
• No answer (Ctrl-C, Ctrl-D, or a closed stdin) — prints No answer given! Exiting without sending. and exits with status 1 without connecting

Both answers log in to Gmail and send a real email containing one randomly chosen message from the list in src/main.py, with the subject Test email from Python. A successful run prints the following and exits with status 0 (with t, the first line reads Logging in with TLS...):

Logging in with SSL...
Login successful!
Email sent to someone@example.com!

If the send fails — an unreachable server, a server that stops responding for 30 seconds, a rejected login, a refused recipient — the reason is printed as Failed to send email: <reason> and the program exits with status 1, so run.sh reports the failure rather than a success. When Gmail rejects the login specifically, a second line follows: Login rejected! Check EMAIL_SENDER_ADDRESS, and that EMAIL_SENDER_APP_PASSWORD is an app password, not the account password. When Gmail refuses the recipient address (for example one with no @), the second line is Recipient refused! Check that EMAIL_RECIPIENT is a valid email address. Pressing Ctrl-C while connecting or sending prints Interrupted! The email may not have been sent. and also exits with status 1.

Tests

The test suite uses the standard library's unittest module and mocks every SMTP connection, so running it sends no email and opens no socket. It replaces the three credential variables with dummy values before loading src/main.py, so credentials exported in the shell are never used by the tests. From the repository root:

python3 -m unittest discover -s tests -t .

Relevant Links

• https://realpython.com/python-send-email/
• https://realpython.com/lessons/sending-emails-intro-and-account-configuration/