Email Server Performance Testing

Timothy Joseph
Timothy Joseph | August 5, 2020

“Discovering the unexpected is more important than confirming the known.”

- George E. P. Box


A survey by Statista revealed that around 293.6 billion emails were sent and received each day in 2019. This is expected to increase to 347.3 billion in 2022.


Why Is Email Server Performance Testing Required?

To check the efficiency of an email server while it's in use.
To identifies any email delivery issues.
To evaluate how much e-mail traffic a server can handle.
To measure the email account's support limit.
To identifies why messages are rejected or undelivered.
To know how the email server handles spam message or message content.


  • Important Protocols

    • SMTP - To send emails
    • POP3 - To read and download emails from email server
    • IMAP - To read and retain emails on email server
  • Key Points: Email Test Data Strategy

    • Email content size
    • Email content type
    • Number of attachments
    • Attachment size
    • Recipients' email addresses

Email Server Performance Testing Cycle

  • SEmail Server Performance Testing Cycle
  • Setup Test Data and Email Client Performance Testing Environment Setup Test Data and Email Client Performance Testing Environment
  • Create scripts (Use tools like JMeter or MultiMail that simulate emails) Create Scripts
    (Use tools like JMeter or MultiMail that simulate emails)
  • Simulate Load Simulate Load
  • Monitor Email Server Performance Monitor Email Server Performance
  • Report Results Report Results

Email Server Performance Testing - Do's and Dont's

Difference Between SAST and DAST
  • Do's

    • Validate test email accounts before test run
    • Keep third-party in sync during test run
    • Test all applicable security settings like SSL/TLS
    • Test POP, IMAP, and SMTP protocols to read and send emails
    • Follow cyber laws and security rules
    • Test various email clients to avoid settings issue
  • Don'ts

    • Use a production IP to avoid high junk mail ratings
    • Avoid same test environment to avoid test emails to real users
    • Ignore network latency
    • Use too much formatting or images in email body
    • Use blacklisted email contact for email relay

Best Practices

Best Practices
  • Avoid spam content to avoid IP address blacklisting
  • Include third party email addresses to certify SMTP relay
  • Include email attachments of various sizes
  • Use a secured port rather than standard ports
  • Use a high-end load generator machine 
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