Swaks
Swiss Army Knife for SMTP — scriptable SMTP transaction testing for engineers.
- Reading time:
- 5 min
- Difficulty:
- Advanced
- Estimated duration:
- 5 min
- Prerequisites:
- None
- Last updated:
- 2026-07-15
- Author:
- empire
Overview
Swiss Army Knife for SMTP — scriptable SMTP transaction testing for engineers.
Vendor: Open source
Primary purpose
Craft and inspect SMTP conversations for debugging delivery paths.
Best for
- Engineers validating SMTP, STARTTLS, and auth behavior
Common use cases
- Test relay permissions
- Reproduce SMTP failures
Advantages
- Precise SMTP control
- Scriptable
Limitations
- Does not score spam content
When not to use it
- Non-technical operators who need a GUI
Pricing
Free open-source utility.
Official website
Inputs and outputs
Typical inputs
- SMTP target
- Message options
Typical outputs
- SMTP transcript
Privacy notes
- Review each vendor’s data handling before uploading production lists or message content.
Related Learn Articles
Related Solve Articles
- Deferred messagesReceivers return temporary SMTP failures (4xx), forcing retries instead of immediate acceptance.
- Delayed deliveryMail eventually arrives but takes much longer than normal due to greylisting, queues, or throttling.
- Emails not deliveredMessages never reach the recipient mailbox — rejected, discarded, or stuck without a successful delivery.
- Hard bouncePermanent delivery failure (typically 5xx) because the address or domain cannot accept mail.
- Soft bounceTemporary delivery failure that may succeed later — full mailboxes, greylisting, or transient outages.