Van's explanation is possible, but much more likely is that your home ISP is blocking sending from a remote location as a security measure to prevent spammers from taking over your account and using it to send spam.
You need to contact your original home Internet provider, the one that maintains your email address, explain you are travelling and ask them for instructions on how to change your SMTP outgoing email configuration to allow sending.
OR
You can opt to just use your home provider's webmail portal to send, receive and manage email while you are away from home
OR
You can set up an IMAP account with iCloud, Google, Yahoo, etc large email provider and use that account, which doesn't care where you are located.