One email or a million, it really makes no difference what software you use. Quite simply, any software capable of sending a single message is capable of sending as many as you like. For the mailing lists I look after I use a simple Perl script.
The software you use is not even a factor in whether you're considered a spammer or not. Just some of the things that do matter are:
- A mailer that doesn't try to fake any message header,
- Proper DNS configuration (reverse pointer and SPF record).
- No virus/malware in the message, or anything that might even trigger a false positive. It only takes one to get you on a blocklist.
- Every message goes out to someone who has voluntarily signed up to the list.
- Use DKIP/Domainkey signing.
- Don't send by CCing to long lists of recipients. One to address per message.
- etc., etc.
Fail on any of those, especially the third, fourth and fifth points, you can pretty much expect to be listed as a spammer, with no sympathy from me.