I need to send newsletters to our customers (nearly 500,000), We are using Google Apps as our mail providers, so ultimately it is Gmail.
I tried several ways of achieving this, but I've run into a couple of problems:
Sometimes, it is hanging up (not sending mails after 255). So I decided to split the emails up into blocks of 255 and tried it again, but this too hangs up once in a while. I can't rely on that.
Also, my clients say that my newsletters end up in their "spam" folder because Google's mail server has labeled them as spam mails.
What can I do to fix this problem?
I would recommend using your own mail server on your own server rather than the gmail server.
But this won't prevent your emails being flagged as spam. It all depends on the recipient's email settings.
You will also have to edit your emails to ensure they do not contain spam related topics and methods because spam filters which check content will mark it as spam.
As you send your emails, you will have to monitor spam block lists to see if your server IP appears on them. If it does, you will have to contact them and apply for your server to be cleared from the block lists.
The good old days of send 10 Million emails is gone. Only the big companies can do it without being blocked.