You can control who is allowed to send emails to a mail group or audience group by configuring its receiving permissions.
Procedure
1. Go to the Domain Admin console. Choose Organization and Users > Mail Group > Mail Group Management. Click the name of the mail group or audience group that you want to modify.

2. On the edit page for the mail group, click the Mail Group Permissions drop-down list and select a receiving permission.

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Configuration |
Description |
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Mail Group Permissions |
Only allow accounts in the same domain to send emails to the mail group |
Only accounts within the same domain can send emails to this mail group. This is the default setting. |
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Only allow mail group members to send emails to the mail group |
Only members can send emails to this mail group. |
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Allow all accounts (both inside and outside the domain) to send emails to the mail group |
Any account can send emails to this mail group. |
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Only allow whitelisted accounts to send emails to the mail group |
Only email accounts on the whitelist can send emails to this dynamic mail group. Whitelist:
The whitelist is limited to 1,000 accounts. |
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Allow mail group members and whitelisted accounts to send emails to the mail group |
Both mail group members and whitelisted accounts can send emails to this dynamic mail group. Whitelist:
The whitelist is limited to 1,000 accounts. |
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