If you are building a mailing list you should use an autoresponder.
I would consider getting a separate domain to use for all mailings you do with the autoresponder. That way if you ever start to have any deliverability issue, it won't be your main domain name.
Make sure you set up SPF. If you don't know what that is, just ask the AR service for help.
Additionally, I would set up seed accounts to test your inbox deliverability.
For many, AOL, Hotmail/Outlook, Gmail, and Yahoo and parent domains using the same mx, can make up as much as 85-90% of their list. So at the very least, you should start with them and any other seed accounts you can set up or acquire.
Also, just get a free trial account to start and test your seeds. If you have any spam folder problems I would complain. If they don't fix, at least you didn't spend any money.