is there any limit within Neomail on the maximum number of outgoing emails that can be sent at a time?

also, another question:

if i use mydomain.com as my mail server, will i be affected if my isp has a restriction on the maximum number of outgoing emails i can send at a time?

I need to send about a hundred new year greetings by tonight and would appreciate your knowledge on this subject.

It depends some hosts has spam control enabled and thus prevent the sending of multiple consecutive emails. What you could do is to break up your greeting emails and send them using smaller package.

If you use your domain as mail server then the mailing rules would be dependent on your host parameters.

Why not ask your host this question?