linkify URLs in plaintext emails.

Cargo.lock

@@ -1747,6 +1747,15 @@ version = "0.2.152"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "13e3bf6590cbc649f4d1a3eefc9d5d6eb746f5200ffb04e5e142700b8faa56e7"
 
+[[package]]
+name = "linkify"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f1dfa36d52c581e9ec783a7ce2a5e0143da6237be5811a0b3153fedfdbe9f780"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.4.13"
@@ -3228,6 +3237,7 @@ dependencies = [
  "async-graphql-rocket",
  "css-inline",
  "glog",
+ "linkify",
  "log 0.4.20",
  "lol_html",
  "mailparse",