feat(backend): relay contact requests to SMTP server

backend/Cargo.lock

@@ -1526,6 +1526,7 @@ dependencies = [
  "tokio",
  "tracing",
  "tracing-subscriber",
+ "validator",
 ]
 
 [[package]]
@@ -1729,6 +1730,28 @@ dependencies = [
  "toml_edit",
 ]
 
+[[package]]
+name = "proc-macro-error-attr2"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "96de42df36bb9bba5542fe9f1a054b8cc87e172759a1868aa05c1f3acc89dfc5"
+dependencies = [
+ "proc-macro2",
+ "quote",
+]
+
+[[package]]
+name = "proc-macro-error2"
+version = "2.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "11ec05c52be0a07b08061f7dd003e7d7092e0472bc731b4af7bb1ef876109802"
+dependencies = [
+ "proc-macro-error-attr2",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.108",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.103"
@@ -2569,6 +2592,36 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b6c140620e7ffbb22c2dee59cafe6084a59b5ffc27a8859a5f0d494b5d52b6be"
 
+[[package]]
+name = "validator"
+version = "0.20.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "43fb22e1a008ece370ce08a3e9e4447a910e92621bb49b85d6e48a45397e7cfa"
+dependencies = [
+ "idna",
+ "once_cell",
+ "regex",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "url",
+ "validator_derive",
+]
+
+[[package]]
+name = "validator_derive"
+version = "0.20.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b7df16e474ef958526d1205f6dda359fdfab79d9aa6d54bafcb92dcd07673dca"
+dependencies = [
+ "darling",
+ "once_cell",
+ "proc-macro-error2",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.108",
+]
+
 [[package]]
 name = "valuable"
 version = "0.1.1"