I'm having the weirdest problem ever. As of this morning, I cannot send e-mail form Mail.app from one of my e-mail accounts on my brand new 13" Macbook Pro. I bought it yesterday, was sending and receiving but at some point around 11am-ish, I started having problems and now it just doesn't send. Now here comes the weird part... 1. I can send from other e-mail accounts 2. I can send from Outlook (but not Mail.app, Sparrow nor Postbox) 3. I can send when I connect to my 3G USB stick 4. I can send from my other 13" Macbook Pro (2009) using Mail.app which is on OS X Lion The problem is my work e-mail, on this new Macbook Pro, on my install of Mail.app as of 11am this morning, it had been working over the last 12 hours before this happened. FYI, I've done it all. Created a new user Repaired permissions Deleted all the preference stuff and re-installed all acounts Rebooted EVERYTHING that's in these forums and nothing has worked. Also, iPhone sends perfectly fine. On WiFi and 3G. Here are the errors that Mail.app shows: (501 Syntactically invalid EHLO argument(s)): READ Sep 14 23:54:59.097 [kCFStreamSocketSecurityLevelNone] -- host:mail.yucatanyes.com -- port:587 -- socket:0x1039a8760 -- thread:0x7f971dddeeb0 220 n19.c06.mtsvc.net ESMTP Exim 4.69 Wed, 14 Sep 2011 21:54:58 -0700 WROTE Sep 14 23:54:59.117 [kCFStreamSocketSecurityLevelNone] -- host:mail.yucatanyes.com -- port:587 -- socket:0x1039a8760 -- thread:0x7f971dddeeb0 EHLO unknown_e4-ce-8f-4d-57-78.gateway.2wire.net READ Sep 14 23:54:59.240 [kCFStreamSocketSecurityLevelNone] -- host:mail.yucatanyes.com -- port:587 -- socket:0x1039a8760 -- thread:0x7f971dddeeb0 501 Syntactically invalid EHLO argument(s) CONNECTED Sep 14 23:54:59.356 [kCFStreamSocketSecurityLevelNegotiatedSSL] -- host:mail.yucatanyes.com -- port:587 -- socket:0x7f971e820870 -- thread:0x7f971dddeeb0 The hells that mean? And why does it work on Outlook and not on the other apps??!!!???!?!