diff --git a/src/input.rs b/src/input.rs
index 9de31f6..df4b77f 100644
--- a/src/input.rs
+++ b/src/input.rs
@@ -29,13 +29,18 @@ pub fn parse_input(input: &str) -> Result<Input> {
 	let mut params_it = input.split(crate::PARAM_SEPARATOR);
 	let stream = next_param!(params_it)?;
 	ensure!(stream == "filter", "{stream}: invalid stream");
-	let _version = next_param!(params_it)?;
-	let _timestamp = next_param!(params_it)?;
-	let _subsystem = next_param!(params_it)?;
+	let version = next_param!(params_it)?;
+	ensure!(!version.is_empty(), "empty version");
+	let timestamp = next_param!(params_it)?;
+	ensure!(!timestamp.is_empty(), "empty timestamp");
+	let subsystem = next_param!(params_it)?;
+	ensure!(subsystem == "smtp-in", "{subsystem}: invalid subsystem");
 	let filter = next_param!(params_it)?;
 	ensure!(filter == "rcpt-to", "{filter}: invalid filter");
 	let session_id = next_param!(params_it)?.to_string();
+	ensure!(!session_id.is_empty(), "empty session id");
 	let token = next_param!(params_it)?.to_string();
+	ensure!(!token.is_empty(), "empty token");
 	let address = next_param!(params_it)?.trim_end();
 	let address = CodedAddress::from_str(address)?;
 	Ok(Input {
@@ -44,3 +49,101 @@ pub fn parse_input(input: &str) -> Result<Input> {
 		address,
 	})
 }
+
+#[cfg(test)]
+mod tests {
+	use super::{parse_input, Input};
+	use crate::address::CodedAddress;
+
+	#[test]
+	fn test_valid_input() {
+		let input = "filter|0.5|1576146008.006099|smtp-in|rcpt-to|7641df9771b4ed00|1ef1c203cc576e5d|derp@example.com";
+		let res = parse_input(input);
+		assert!(res.is_ok());
+		let inp = res.unwrap();
+		assert_eq!(inp.session_id, "7641df9771b4ed00");
+		assert_eq!(inp.token, "1ef1c203cc576e5d");
+	}
+
+	#[test]
+	fn test_empty_input() {
+		assert!(parse_input("").is_err());
+	}
+
+	#[test]
+	fn test_empty_stream() {
+		let input = "|0.5|1576146008.006099|smtp-in|rcpt-to|7641df9771b4ed00|1ef1c203cc576e5d|derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_invalid_stream() {
+		let input = "invalid|0.5|1576146008.006099|smtp-in|rcpt-to|7641df9771b4ed00|1ef1c203cc576e5d|derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_empty_version() {
+		let input = "filter||1576146008.006099|smtp-in|rcpt-to|7641df9771b4ed00|1ef1c203cc576e5d|derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_empty_timestamp() {
+		let input =
+			"filter|0.5||smtp-in|rcpt-to|7641df9771b4ed00|1ef1c203cc576e5d|derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_empty_subsystem() {
+		let input = "filter|0.5|1576146008.006099||rcpt-to|7641df9771b4ed00|1ef1c203cc576e5d|derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_invalid_subsystem() {
+		let input = "filter|0.5|1576146008.006099|invalid|rcpt-to|7641df9771b4ed00|1ef1c203cc576e5d|derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_empty_phase() {
+		let input = "filter|0.5|1576146008.006099|smtp-in||7641df9771b4ed00|1ef1c203cc576e5d|derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_invalid_phase() {
+		let input = "filter|0.5|1576146008.006099|smtp-in|invalid|7641df9771b4ed00|1ef1c203cc576e5d|derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_empty_id() {
+		let input =
+			"filter|0.5|1576146008.006099|smtp-in|rcpt-to||1ef1c203cc576e5d|derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_empty_token() {
+		let input =
+			"filter|0.5|1576146008.006099|smtp-in|rcpt-to|7641df9771b4ed00||derp@example.com";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_empty_data() {
+		let input =
+			"filter|0.5|1576146008.006099|smtp-in|rcpt-to|7641df9771b4ed00|1ef1c203cc576e5d|";
+		assert!(parse_input(input).is_err());
+	}
+
+	#[test]
+	fn test_missing_data() {
+		let input =
+			"filter|0.5|1576146008.006099|smtp-in|rcpt-to|7641df9771b4ed00|1ef1c203cc576e5d";
+		assert!(parse_input(input).is_err());
+	}
+}