Mail handler parsing problem

Hi everyone,

I'm currently facing a problematic of non parsing incoming mail to jira.
Mail handler configuration was done and it worked for weeks without any problems. I encountered a problem with a first mail and then all following ones are not correctly parsed. Issue is created, subject is correctly set but the description contains the mail header, as raw data (attached screenshots)

I tried restarting jira, we deleted the mail handler and recreated it and none worked so far. We were not able to reproduce that problematic on the test environment that features the same jira setup and configuration. Both servers use the same mail server but different accounts.

In the logs, not much I'm afraid, we once had a :
com.sun.mail.util.DecodingException: BASE64Decoder: Error in encoded stream: needed at least 2 valid base64 characters, but only got 1 before padding character (=), the 10 most recent characters were: "peg; name="
at com.sun.mail.util.BASE64DecoderStream.decode(BASE64DecoderStream.java:266)
at com.sun.mail.util.BASE64DecoderStream.read(BASE64DecoderStream.java:144)
at java.io.FilterInputStream.read(FilterInputStream.java:107)
at javax.activation.DataHandler.writeTo(DataHandler.java:308)
at com.atlassian.jira.plugins.mail.handlers.AbstractMessageHandler.getFileFromPart(AbstractMessageHandler.java:1182)

I'm attaching the atlassian-jira.log if that helps.

I'm currently asking for recommendations and your assistance.

Thanks in advance.