Bump com.icegreen:greenmail from 2.1.0-alpha-3 to 2.1.0-alpha-4 (#612)

Bumps [com.icegreen:greenmail](https://github.com/greenmail-mail-test/greenmail) from 2.1.0-alpha-3 to 2.1.0-alpha-4.
- [Release notes](https://github.com/greenmail-mail-test/greenmail/releases)
- [Commits](greenmail-mail-test/greenmail@release-2.1.0-alpha-3...release-2.1.0-alpha-4)

---
updated-dependencies:
- dependency-name: com.icegreen:greenmail
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pom.xml

@@ -959,7 +959,7 @@ under the License.
       <dependency>
         <groupId>com.icegreen</groupId>
         <artifactId>greenmail</artifactId>
-        <version>2.1.0-alpha-3</version>
+        <version>2.1.0-alpha-4</version>
         <exclusions>
           <exclusion>
             <groupId>com.sun.mail</groupId>