fix #694 by forking lettre and avoiding extra NOOP Smtp commands for connection checking.

If this works out and fixes our problem, we can submit upstream.

Cargo.lock

@@ -500,7 +500,7 @@ dependencies = [
  "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "jetscii 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "lettre 0.9.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lettre 0.9.2 (git+https://github.com/deltachat/lettre)",
  "libc 0.2.62 (registry+https://github.com/rust-lang/crates.io-index)",
  "mmime 0.1.2",
  "native-tls 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1072,7 +1072,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "lettre"
 version = "0.9.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
+source = "git+https://github.com/deltachat/lettre#aeec999c27a70870e4b7b149e45f24188c1ff351"
 dependencies = [
  "base64 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "bufstream 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1080,7 +1080,7 @@ dependencies = [
  "hostname 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "native-tls 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "nom 4.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "nom 5.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.40 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2968,7 +2968,7 @@ dependencies = [
 "checksum keccak 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "67c21572b4949434e4fc1e1978b99c5f77064153c59d998bf13ecd96fb5ecba7"
 "checksum kernel32-sys 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "7507624b29483431c0ba2d82aece8ca6cdba9382bff4ddd0f7490560c056098d"
 "checksum lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e2abad23fbc42b3700f2f279844dc832adb2b2eb069b2df918f455c4e18cc646"
-"checksum lettre 0.9.2 (registry+https://github.com/rust-lang/crates.io-index)" = "c66afaa5dfadbb81d4e00fd1d1ab057c7cd4c799c5a44e0009386d553587e728"
+"checksum lettre 0.9.2 (git+https://github.com/deltachat/lettre)" = "<none>"
 "checksum lexical-core 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)" = "2304bccb228c4b020f3a4835d247df0a02a7c4686098d4167762cfbbe4c5cb14"
 "checksum libc 0.2.62 (registry+https://github.com/rust-lang/crates.io-index)" = "34fcd2c08d2f832f376f4173a231990fa5aef4e99fb569867318a227ef4c06ba"
 "checksum libsqlite3-sys 0.16.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5e5b95e89c330291768dc840238db7f9e204fd208511ab6319b56193a7f2ae25"

Cargo.toml

@@ -19,7 +19,7 @@ reqwest = "0.9.15"
 num-derive = "0.2.5"
 num-traits = "0.2.6"
 native-tls = "0.2.3"
-lettre = "0.9.0"
+lettre = { git = "https://github.com/deltachat/lettre" }
 imap = { git = "https://github.com/jonhoo/rust-imap", rev = "281d2eb8ab50dc656ceff2ae749ca5045f334e15" }
 base64 = "0.10"
 charset = "0.1"