Question 1

What is the SMTP Response Decoder tool used for?

Accepted Answer

The SMTP Response Decoder tool tests your email server configuration by attempting a real connection to the specified SMTP, IMAP, or POP3 server. It checks connectivity on standard ports (25, 465, 587, 993, 995), verifies STARTTLS or SSL/TLS support, tests authentication, and reports any connection errors. This is essential for troubleshooting email sending failures, verifying hosting provider configuration, and auditing server security.

Question 2

What SMTP ports should I use and when?

Accepted Answer

Port 25 is the original SMTP port for server-to-server mail transfer — most ISPs block outbound port 25 for clients. Port 587 (STARTTLS) is the recommended port for email client submission — it starts unencrypted then upgrades to TLS. Port 465 (SMTPS) uses SSL from the start and is supported by most modern clients. Avoid port 25 for sending from applications; use 587 with STARTTLS or 465 with SSL for all authenticated sending.

Question 3

Why is my SMTP connection being refused?

Accepted Answer

SMTP connection refused errors are commonly caused by: (1) Wrong server hostname or port — double check your email provider's settings. (2) Firewall blocking the port on your server or network. (3) The mail service is down. (4) Your IP is blacklisted and the server is rejecting connections. (5) TLS/SSL mismatch between client and server settings. Use our SMTP Tester to narrow down which step fails.

Question 4

What is the difference between SMTP, IMAP, and POP3?

Accepted Answer

SMTP (Simple Mail Transfer Protocol) handles sending and delivering email between servers. IMAP (Internet Message Access Protocol) is used by email clients to retrieve and sync messages from a mail server while leaving them on the server — ideal for multi-device access. POP3 (Post Office Protocol 3) downloads messages to the local device and typically removes them from the server. Most modern email clients and apps use IMAP. Use our IMAP Tester or POP3 Tester to verify server connectivity.

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