Recomendation on adding trusted domain

[Shusovit Dutta]

There is a requirement to add 5000+ trusted domains in the system, so that inbound emails can be processed. But I feel this should not be done due to risks like performance degradation, Security Vulnerabilities, spam emails etc. What else can be the risks that makes this requirement a not recommended one. 

[Vasantharajan N]

@Shusovit Dutta - Why don't you use the "Email Address filter" to accept and process the emails only from the trusted domains.