This error is not given by Outlook but by your ISP or corporate mail administrator. Usually you get a Send/Receive error or you’ll get an email message back from Administrator, or similar, containing a notification with error 4.5.3 or “452 too many recipients”.

Outlook itself doesn’t hold a limit for the amount of addresses that you can send to within a single email. ISPs or corporate mail administrators usually have one of the following limits set or a combination of them;

1. amount of recipients for a single email
2. amount of emails that you can send in an hour


3. amount of emails that you can send in a day

These limits are set to protect their mail server from excessive use or even abuse by spammers. You’ll have to contact your ISP or corporate mail administrator to find out which exact email policies they have in place.

Once you know them, then you can use different methods to comply with them. Some suggestions;

1. For the first limitation you can use a mail merge.

2. For the second limitation you can use a mail merge addin which automatically breaks the mail merge into batches which are each below this limit. Several of these tools are also discussed in the mail merge guide.

3. For the third limitation you could also use the method for the second limitation but that often doesn’t make any sense when sending out a time-bound mailing. In that case, you could consider using a third party service for mass mailings. Your local copy shop might also provide these services to you.

4. Usually when you have a business subscription with your ISP, you won’t have any such limitations but it could also require an upgrade of your subscription. Ask your ISP about the possibilities.

5. Your corporate administrator could also have designated a specific mail address which you can use to send out large mailings or can temporary remove these limitations for your account or schedule it to run at night.