I've been requested to search for a way to send 4,000 emails and it would be easier to send them all at once; it's going to be some info about a conference and they have the medics' email addresses.

I'm wondering if you could help me by telling me some companies or software or online apps or whatever would be helpful in this case.

I'll be doing my research too, so i'll post what i find out too.

Thanks in advance.