As the message suggests, only recipients associated with your sign-up account or verified domain are permitted in the CSV file.

If your domain isn't verified, you can still upload the CSV file, but it's limited to a maximum of =5 employees with the same domain.

However, we don't allow any employee that does "not" belong to the domain put in the csv file. They must belong to the specfied domain.

To verify the domain, please go to Trend Vision One console > Phishing Simulation Assessment > Edit Settings > Domain Verification

For reference, kindly see: Verifying Domain Ownership

1. Confirm that the user is using the CSV template file download from: Phishing Simulation Assessment > Recipient Data Source > Csv template: Download
2. Try using a different browser, such as Microsoft Edge or Chrome, to see if the issue persists.

The limitation is 4 MB for CSV upload, which is around 15,000 users. There are no limitations for AD Sync.

There are no limits to the number of times a simulation campaign can be conducted.

It could be that the internal network of that company restricted the connection.

The following allow list setup may help:
To do this, go to Trend Vision One console > Phishing Simulation Assessment > Edit Settings > Allow List Settings

For reference, kindly refer to: Phishing Simulation Assessment General Allow List Settings

The phishing assessment tool currently allows for editing the sender's name, subject, and content text. However, image upload is currently not supported.

The editor enhancement with more comprehensive functions is on the roadmap but without a definite timeline.