If you are just doing cold mailing on one-to-one basis, you can use migadu.com for it. Everyone has to do that at some point and it is not spam. 500 mails is not a lot. Just cap it daily to e.g. 50-100 or you could hurt your own domain reputation.
> Email spam, also known as junk email, refers to unsolicited email messages, usually sent in bulk to a large list of recipients.
> Email spam, also known as junk email, refers to unsolicited email messages, usually sent in bulk to a large list of recipients.