For the Sieve Email Filtering Language, yes. Which is not actually part of SMTP. And even in RFC 5233 the specific separator sequence is up to the server; the R

For the Sieve Email Filtering Language, yes. Which is not actually part of SMTP. And even in RFC 5233 the specific separator sequence is up to the server; the RFC only specifies queries for ":user", ":detail", and ":localpart" to filter on the different fields independent of the choice of separator.