There are a number of anti-spam blacklist used to battle spam. If spam was recently sent from your network, it is possible that your email will not be delivered and you will get no errors as it may get deleted on the other end.
To determine if you are on a blacklist, go to:
This provides the IP address you are currently using to connect to the internet. Copy that address and then go to:
and enter your IP address. If you see that your network is listed on a blacklist you will need to try to get a new address.
To get a new IP address, please restart your modem/router (the device that connects you to your local internet service provider) which should assign a new address, then check to see what address you are on using whatismyip.com again and then use that number to run another check to see if it is listed. If so, repeat the above until you get a clean address.
If this is a regular problem, you should talk to your internet service provider about keeping spammers off of their network.
In some cases you can request removal from the various blacklist. In some cases your ISP will need to make that request.