The phrase "mail-cheeked" is a poetic way of describing someone with a strong or resilient face. If you're looking for synonyms to use instead, there are a few options. For example, you could say someone has a stoic expression or a poker face, both of which suggest a certain unflappable quality. Another possibility is to say someone looks resolute or determined, indicating a strong sense of willpower. Finally, you could describe someone as having a steadfast or unyielding demeanor, emphasizing their refusal to be swayed or intimidated. All of these synonyms capture the essence of mail-cheeked without using the exact phrase itself.