Bump greenmail from 1.6.3 to 1.6.4

Bumps [greenmail](https://github.com/greenmail-mail-test/greenmail) from 1.6.3 to 1.6.4.
- [Release notes](https://github.com/greenmail-mail-test/greenmail/releases)
- [Commits](https://github.com/greenmail-mail-test/greenmail/compare/release-1.6.3...release-1.6.4)

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/modules/transport/mail/pom.xml b/modules/transport/mail/pom.xml
index a770bc0..661c715 100644
--- a/modules/transport/mail/pom.xml
+++ b/modules/transport/mail/pom.xml
@@ -123,7 +123,7 @@
         <dependency>
             <groupId>com.icegreen</groupId>
             <artifactId>greenmail</artifactId>
-            <version>1.6.3</version>
+            <version>1.6.4</version>
             <scope>test</scope>
         </dependency>
     </dependencies>