Problem with your ISP mail relay not recognized anymore ?

Wednesday, September 02 2009 @ 08:38 AM UTC

Contributed by: Admin

You are hit by an Mail.app error telling you that your ISP mail relay doesn't respond anymore when it had always worked before ?

Think to flush the DNS cache…

Either by changing the DNS settings in System Preferences/Network… (remove the IPs in DNS field, click Apply, …)

Either by executing in Terminal (for Leopard)


sudo dscacheutil -flushcache
Maybe not the solution to all the use cases, but this saved some days here… For those of you beaten by the upgrade to Snow Leopard and the "not able to send mails anymore" problem, here is our advice:

1. look at your ISP possible settings and if your ISP allows SMTP connection with authentication use this configuration instead of the classical "no authentication" one used by most people having a DSL connection for which authentication is implied by the fact to be physically wired to the ISP…
2. among the authentication methods allowed, give priority to the most secure one (with SSL if allowed by your ISP)
3. in case no SMTP with authentication is available, force the port to 25 instead of the automatic discovery mechanism
4. always end-up the modification of settings by leaving Mail.app, flush the DNS cache in Terminal and re-lauch Mail.app again.

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