From Google: "You have reached a limit for sending mail" You may see this message if you send an email to a total of more than 500 recipients in a single email and or more than 500 emails sent in a day. When you get this error, you should be able to send emails again within 1 to 24 hours.

Also Google: For individual Gmail accounts, the daily send limit is 500 emails per rolling 24-hour period. If you're a typical Gmail user, you may not even know about this limit because it's doubtful you send that many emails in a typical day. But note, Google counts each email address as a separate email, so one message sent to five recipients would count as five emails.

For Google Workspace accounts (formerly G Suite), the daily sending limit is 2,000 emails per rolling 24-hour period, per email address. These accounts are usually for businesses and operate under the company's domain, such as AmalgamatedWidgets.com, but they use the same Google email (Gmail) technology.

The recipient's email server may also have quotas and/or spam filters that blacklist senders suspected of spamming.  To ensure delivery, you need to ask every one of your recipients to "white list" your email address at their end.  These hassles are why email is no longer the go-to messaging method that it used to be.

Thanks for your guidance. I am working my way through the Email Seminar. I would like to schedule a future date and time to start sending bulk emails.

Can I tell the system to send my newsletter, for example, on April 21 beginning at 09:00? Assume I have 1,000 emails to send. I would like it to send a maximum of 200 emails per day beginning at 09:00. The emails would be sent out over a 5 day period.

You'd have to use a timer event to check for what time it was and program which emails to send, I'd probably be more inclined to just use a button and push it manually though.

I did mass-emailing in my old job and found that I could only send at most 10 emails (each recipient counts as one email) every 10 minutes.  Any higher frequency than that would make us blacklisted by the email server at the origin or destination, or both, and we wouldn't be able to send anything for hours (exact duration varies among different servers).  You may be lucky and deal with servers that are more forgiving.  But when you send mass emails, you can only do it at a frequency that the *strictest* server allows.  Also, some servers may "shadow ban" you, meaning they may block you without sending you any "failed delivery" notices, so you'll be completely in the dark.  That was why in my old job, every time I sent out a big batch of email there were always a few people who said they didn't get it.  At 10 emails per 10 mins, you need 200 minutes to send 200 emails, so it is a manageable task.  You still need to do your own testing to find out the exact, right frequency for you.  In my old job, we had to send thousands of emails at a time, and had to leave the computer on all night.  And if you wonder how companies send you tons of marketing emails that you see everyday, they use paid bulk email services.

If memory serves, I don't think I cover scheduling emails to start going out at a particular date and time, but that shouldn't be too hard to add. If you understand the rest of the seminar that's a piece of cake; it's a basic timer. The mail server that we build in the seminar just has a queue, and you can specify how often you want those emails to go out (delay). So, if you are running into a problem like Gmail and the allowance of 500 per day, you won't run into their limits.

I use Gmail for most of my day-to-day correspondence, customer service emails, and even personal contacts. However, I don't use it for bulk mail sending because I've got 50,000 people on my mailing list. So, I use a paid account over at SendGrid.com, which I believe is now owned by Twilio. I use that for all my bulk mail stuff, such as sending out mass customer notifications for the one or two sales I have every year. Things like that, I wouldn't use Gmail for.  

At one point years ago, when I was first starting out, I thought I'd be smart and set up multiple Gmail accounts and some Yahoo accounts. I built a mail server database to rotate between those accounts, but they got smart and they saw those emails coming from my IP address. They banned most of them, so don't try getting around them; they're smarter than we are. LOL.

If you're going to be doing a lot of bulk mail, just pay for it. I think over the last holiday season, I sent out over 150,000 emails and it cost me like $34, so it's not a lot. It's more incentive to keep your mailing list clean, too. Pruning those unsubscribes and dead email addresses is important.