How do I add TLS domains in Exchange Online Protection

I need to configure a number of domains for TLS encryption in Exchange Online Protection. I run Exchange 2007 on-premise and use EOP for security. I think the only way to do this is through an EOP transport rule. So I ran the following commands:

$TLSList = Import-CSV -Path "c:\temp\TLSDomains.csv" | Select-Object -ExpandProperty Domains
New-TransportRule -Name "Global TLS Domains List" -RecipientDomainIs $TLSList -RouteMessageOutboundRequireTls $true

I get the following error:
The rule can't be created because it is too large. It has 11502 characters, and the maximum number of characters is 4096. Reduce the size, either by removing content, such as words or regular expressions, from the rule; or by removing conditions, exceptions, or actions from the rule.

The TLSDomains.csv file contains over 250 domains. Is this a limit I can increase or do I have to create multiple rules?

Am I doing this the right way or is there another place to add my TLS domains?

Thank you.