Actually you don't want identical settings on the iPhone, which Apple warns against in the manual.
Do you have a section or page number in the manual where it indicates this because I don't recall seeing it or I missed it.
The option to sync email account settings via the iPhone sync preferences with iTunes syncs or transfers the same account settings from your computer to the iPhone. This can work depending on the IPS used for connecting to the internet but it is usually the ISP being used for the internet connection that has the restrictions on using an SMTP server that is outside of their network.
Apparently Comcast is the OP's ISP so if the OP has a wireless network at home using Comcast for the internet connection and is able to send messages with the computer's email client but not with the iPhone using the same settings when connected to the internet with Comcast, something may have gone wrong with account settings transfer to the iPhone which is why deleting and manually creating the account on the iPhone is the next step to take if this is the situation.
I use the identical SMTP server settings with my .Mac account, my business POP account and my Gmail IMAP account but each has its own SMTP server which is authenticated. Many ISPs will allow the use of an SMTP server that is outside of their network as long as the SMTP server is authenticated. Some block using Port 25 for an SMTP server that is outside of their network regardless if the SMTP server is authenticated or not and in that case, using 587 for the Server Port using works.
