Python Email Attachments: Filenames, Types, and Sizes

An attachment has both content bytes and metadata such as media type and filename.

Why This Matters

Connect the protocol to its actual role. SMTP is for submission, IMAP/POP are for retrieval, while FTP is a separate file-transfer protocol. Authentication and transport encryption are separate concerns.

In this lesson, the focus is Email Attachments: Filenames, Types, and Sizes. The aim is to understand its inputs, observable behavior, and a realistic situation where it is useful, rather than memorize a command name.

How the Example Works

get_payload(decode=True) returns attachment bytes, not a safe filesystem path. Use a trusted destination name if saving it.

Step-by-Step Example

from email.message import EmailMessage
message = EmailMessage()
message.set_content("Attached: quarterly data")
payload = b"name,total\nKay,15\n"
message.add_attachment(payload, maintype="text", subtype="csv", filename="sales.csv")
for part in message.iter_attachments():
    print(part.get_filename(), part.get_content_type(), len(part.get_payload(decode=True)))

Understanding the Result

The program starts by importing email.message, making the needed interfaces available.
Watch these operations in order: EmailMessage, message.set_content, message.add_attachment, message.iter_attachments. The arguments and return values are the central parts of the demonstration.
Determine whether this sample only builds/parses a message or would actually contact a remote service. A constructed message is not a delivered message.

Observed Output

sales.csv text/csv 18

This output was produced by the example in the available local Python test environment. Output that depends on the operating system, time, installed packages, or object representations may differ on your computer.

Important Details and Limitations

A declared media type does not prove actual file contents. Enforce limits on count and size.

Can your test be completed without contacting an account or service? Prefer constructing a message or parsing sample bytes locally before integrating with a mail provider.

Try It Yourself

Reject attachments larger than a simulated 1 MiB limit.

Before running the modified example, write down what you expect to happen. Test one normal case and one boundary, missing-input, or invalid case when the operation accepts them.

Common Beginner Mistakes

Assuming Email Attachments: Filenames, Types, and Sizes behaves the same way with missing, malformed, or unsupported inputs as it does in the worked example.
Ignoring this requirement: A declared media type does not prove actual file contents.
Treating a small illustrative snippet as a production-ready program without testing failures, cleanup, and the target environment.

Key Takeaways

An attachment has both content bytes and metadata such as media type and filename.
get_payload(decode=True) returns attachment bytes, not a safe filesystem path.
To confirm understanding: Reject attachments larger than a simulated 1 MiB limit.