Anthony,
You'll want to avoid using a 1024 bit key size, this key size has been deprecated by most major providers. You will want to use 2048 bit.
Both Microsoft DNS and standard BIND DNS servers will encounter this issue.
You'll need to break up the 2048 bit DKIM key into multiple lines. For example instead of having a DKIM key that resembles the following:
p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC2HUa40zk+1xuJPje3Dxf1NwrVP0apSJnaJNCuG6U5iiVCx8RXhiCJlldIbkh1glfhJijZDpuQ7W6QE9By1/5u7ArfmzqRB5QlgfpFlPdYGDLSBeBFSbkPF3jK6izChZNRwS8lcQdGtD/09wHuVZBfO1V+jOL8+JlHWJC5y7hdLwIDAQAB
You'll want to add line breaks to the record so that it resembles the following:
p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC2HUa40zk+1xuJ
Pje3Dxf1NwrVP0apSJnaJNCuG6U5iiVCx8RXhiCJlldIbkh1glfhJijZDpuQ7W6
QE9By1/5u7ArfmzqRB5QlgfpFlPdYGDLSBeBFSbkPF3jK6izChZNRwS8lcQd
GtD/09wHuVZBfO1V+jOL8+JlHWJC5y7hdLwIDAQAB
I hope this helps.
Von See
Technical Support Supervisor
SmarterTools Inc.
(877) 357-6278
www.smartertools.com