Cannot send mail on the road

Question

I am on the road and in some cases have to pay for internet privileges. I can receive mail and surf the internet with Safari. But I cannot send any mail and get the error message. The clerk at the motel here says to change the outgoing mail server to their server provider. But nothing good happens for me when I do that and restart. I tried to repair permissions and restarted several times.
The problems always seem to take place on locked WiFi. Open WiFi like Panera Bread I can access and send mail usually with no problem as well at the occasional open WiFi you run across from time to time.
G4 Powerbook & iMac 800   Mac OS X (10.4.5)  
G4 Powerbook & iMac 800   Mac OS X (10.4.5)  
G4 Powerbook & iMac 800   Mac OS X (10.4.5)  
G4 Powerbook & iMac 800   Mac OS X (10.4.5)  
G4 Powerbook & iMac 800   Mac OS X (10.4.5)  
G4 Powerbook & iMac 800   Mac OS X (10.4.5)  

Answer 1

Most if not all internet service providers used for connecting to the internet now block the use of SMTP servers that are outside of their network (or not provided by the ISP) on Port 25 which is the default port used for SMTP servers.
Some ISPs allow the use of an authenticated SMTP server only that is outside of their network on Port 25 but some ISPs block its use regardless.
These restrictions are in place as part of an overall effort to prevent spam emanating from the ISP's domain and to have better control over customers that violate the ISP's terms of use in regards to sending email.
You can try changing the server port for the SMTP server from 25 to 587 and if this doesn't work, your only option is adding the ISP's SMTP server in Mail as an available SMTP server to choose from to be used to send messages with an email account not provided by that ISP. If this isn't allowed or doesn't work either, your only other option is sending messages via webmail access using a browser which doesn't use an SMTP server to send messages.
Go to Mail > Preferences > Accounts and under the Account Information tab for your email account preferences at the SMTP server selection, select the Server Settings button below. Enter 587 in place of 25 in the Server Port field and when finished, select OK to save the changed setting.
In my experience when staying at a hotel that provides free wired and/or wireless internet access, after entering the password for access provided at the front desk when checking in, I don't have problems sending messages with my .Mac account and .Mac's authenticated SMTP server which I now use as my primary personal email account. The last hotel I stayed in which was out of state happened to use the same ISP that I use at home but this was the first and only time I've come across this.
Basically it is up to the internet service provider being used to connect to the internet at the time. Some ISPs have identical restrictions in regard to using an SMTP server that is outside of their network but some are different. Since hotels/motels that provide free internet access can't expect their customers to have the same ISP and depending on the hotel/motel have business travelers that need access to sending email with their business email account using an email client such as Mail that requires using an SMTP server that is not provided by the ISP, this should be a no-brainer for the hotel and the hotel's ISP but we can thank spammers for these problems.