The problem was of these dependencies: simplejavaemail 6.4.4 and atlassian-renderer 8.0.30

simplejavaemail 6.4.4 depens on org.simplejavamail (core-module) 6.4.4 which uses jakarta.activation 1.2.1

atlassian-renderer 8.0.30 depens on javax.activation 1.0.2

jakarta.activation 1.2.1 includes package name javax.activation and com.sun.activation.registries.MailcapFile.getMailcapList returning Map

javax.activation 1.0.2 com.sun.activation.registries.MailcapFile.getMailcapList returning Hashtable

com.atlassian.renderer 9.0.3 the first version of artifact which depends on javax.activation 1.1.1, the older versions depens on javax.activation 1.0.2

javax.activation 1.1.1 com.sun.activation.registries.MailcapFile.getMailcapList returning Map as well

Since version 7.0.0 of simplejavamail (core-module) up dependency of jakarta.activation (2.0.1) which is using another namespace jakarta.activation and it does not overlap with javax.activation