This indicates an attack attempt to exploit an Out Of Bounds Read Vulnerability in Dovecot.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted SMTP packet. An attacker can exploit this to disclose arbitrary files or cause a denial of service condition on the affected machine via a crafted SMTP packet.
Dovecot Prior to 2.2.34
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Denial of Service: Remote attackers can crash vulnerable systems.
Apply the most recent upgrade or patch from the vendor: