Gmail
Max 500 destinatari ogni 24 ore, 500 o 100 per ogni messaggio a seconda del programma usato (web gmail o client application)
What is Gmail’s Daily Limit on Sending Email? 
Linee guida per mittenti di messaggi collettivi
Numero massimo di destinatari 
Esiste un limite relativo ai destinatari ai quali si può inviare un singolo messaggio: una singola email può essere infatti inviata a massimo 100 destinatari per volta, ma questo limite si applica solo se si utilizza un client di posta elettronica tipo Outlook: se si accede a Gmail da web, questo limite non sussiste! Rimando a tal proposito al link in Riferimenti, che illustra anche gli altri limiti: 500 destinatari al giorno massimi in totale, indipendentemente da cosa si utilizzi per accedere a Gmail!How many emails can you send in Gmail at a time?
The current Gmail email sending limit is 500 emails per 24 hours when sending from their web interface.
It’s important to note that this means 500 in any combination (i.e. 1 email to 500 people or 5 emails to 100 each, etc.).
...
If you’re sending from a desktop email client, that limit is much smaller – 100-150 emails per 24 hours, depending on the size of the emails.
New limit imposed on max. number of addresses per message?
Hello,
Gmail used to have a limit of 500 recipients per email message (or 100 if sent from an email client program).
I send weekly emails to a list of about 50 addresses. All was fine, until this week. This week's message bounced saying that the message was "blocked" to every single address, including my own. I received 50+ bounces, one per address.
After a few days of retrying, and looking for an explanation, I finally resorted to sending separate emails to everyone on the list, and they all went through, no problem. Golly.
But I got lazy near the end of the list, and my last message was addressed to 11 recipients -- and that one bounced. When I split it into two messages with half as many recipients each, they both went through. Therefore, I conclude that someone at Google has throttled the threshold down from 500 to about 10.
When the limit is exceeded, the bounce message is cryptic, saying little more than the fact that the message has been "blocked", and refers to https://support.google.com/
For example:
Final-Recipient: rfc822; someone@comcast.netAction: failedStatus: 5.0.0Diagnostic-Code: smtp; Message rejected. See https://support.google.com/mail/answer/69585 for more information.
followed by a severely truncated version of my email message, and no further diagnostic information.
In case it matters, messages were sent from Gmail's web interface (client software not involved), on Chrome.
What's going on? Has there been an announcement about such a change? Does it sound like a bug?
Thanks,
Andy
-----------------------
Hi Andy,
That has been happening to me as well. It started a several months ago, but I would split my list to 40 recipients and all would be fine. Then after a few days, no problem I can send out to my email group of 125 with no problem until it happens again. Recently, some messages are blocked and others aren't. Some group messages retry delivery over a period of time which results in multiple blocked replies for each recipient. At first I thought it was because of the graphics in my message, but even that is not consistently blocked.
I find if I send to small group of 2 or 3, it's fine. But that is too much of a hassle.
Once I received a link that suggested I create a google group. But that is not what I want to do. My group emails are notifications and I want to keep it as such.
And I don't want to subscribe to an email client.
Yes, it appears the messages are blocked internally by google.
Andy, I'm glad you've posted as I want to understand what is going on, too.
Sending Gmail to Groups and being seen as Spam