Email not sending: how to troubleshoot the delivery path
“Email not sending” can mean a message never left the email app, SMTP authentication failed, the sending server rejected it, the recipient server rejected it, or the message was accepted but filtered later. Preserve the exact error before changing settings.
Start with where the failure is visible
A message stuck in an Outbox, a webmail error, a website contact-form failure, and a bounce message come from different layers. Reproduce the problem from one known client and record the timestamp and full error text.
Verify SMTP identity, port, and TLS
Confirm the outgoing hostname, port, encryption setting, full username, password, and whether the provider requires authentication. Receiving mail through IMAP does not prove SMTP submission is correct.
Check account and network restrictions
Mailbox suspension, password changes, sending limits, blocked ports, firewall rules, or provider anti-abuse controls can stop submission even when the configuration used to work.
If the server accepted it, follow the bounce or delivery evidence
Once the sending service accepts the message, inspect its logs or delivery status. A recipient rejection, spam placement, DNS authentication problem, or reputation issue requires a different fix than an SMTP login failure.