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A possible fix for not sending email Apps
My wife and I (and others) have had an issue with where the message will get to a certain percentage completed sending and then stop. Eventually it will time out and a message about how the SMTP server didn't work, would you like to try another? We could never get it to reliably work with another one. Rebooting usually worked for my wife, but I didn't like losing my apps. So I would just wait, and it would eventually work (sometimes right away after restarting Mail).

I decided that it might be something getting hung with that particular server. Our ISP (as with most big ones, I'm sure) will load balance across several physical machines, so might resolve to quite a few different addresses over time. OS X caches these addresses. So the fix seems to be to get the cache flushed and hope for a different machine. It's worked for us the several times we've tried it.

Using info from previous hints about how to call a shell script from AppleScript, and a command from this previous hint (I used the command from the first comment) to actually flush the cache, I've come up with the following solution. Put the below command in an AppleScript, and put the script in your Library -> Mail Scripts folder, refresh the scripts menu and you're ready the next time it fails.
do shell script "lookupd -flushcache"
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A possible fix for not sending email | 6 comments | Create New Account
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A possible fix for not sending email
Authored by: Kickaha on Aug 11, '04 11:38:31AM

We had the same problem with Telocity a couple of years ago - I was able to pinpoint the one server in their pool that was bad. (It was their one remaining MS-based mail server. Go figure.) A simple reboot of that server fixed it for them. Convincing them I wasn't trying to hack into their systems took longer than the fix, I swear.

Nice workaround for the client end though.

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MTU settings
Authored by: chrome on Aug 11, '04 02:55:22PM

My home router has an MTU of 1492. It plays hell with my mac, and I get similar problems to you.

A temporary fix is to sudo ifconfig en1 mtu 1400. (if en1 is your active interface)

Give it a go. It might work ;)

Lowering the MTU permanently is on my list of things to figure out for OSX, but I'm not sure where to start.

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MTU settings (duex)
Authored by: wsdr on Aug 11, '04 05:39:56PM

Many routers allow you to change the MTU, and some DSL modems (Bellsouth) require the MTU to be 1492 or lower. We ran in to similar problems with LinkSys routers which defaulted to MTU of 1500. Changing the router's MTU to 1492 (or 1400, anything under 1493) solved the problems.

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MTU settings
Authored by: MrPhil on Aug 12, '04 12:38:13PM

Wouldn't the MTU problem show up with other network activity? The mail sending is the only problem we have.

Running the script changes what address the mac uses for and seems to fix the problem. I am going to start watching to see which bugger is the problem.

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MTU settings
Authored by: Melton on Aug 13, '04 04:50:42AM

In Panther (10.3), go to your Network System Preference, select the Ethernet button and adjust your MTU there.

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A possible fix for not sending email
Authored by: o_sleep on Aug 12, '04 10:00:59PM

What I have run into is servers being cached as inaccessible. You can't ping them until I restart lookupd. For some reason turning off lookupd's cache doesn't help.

You could try turning off lookupd's cache for your problem though. Refer to the man page or:

you can do this either with a file or by using netinfo to turn off lookupd's cache.

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