Error <<< -ERR Server Unavailable. 21

[sdlsystems]

Hello everyone.

Since this morning, i cant fetch emails from Office365 acounts with Oauth authentication.

I recive this error:

Net::POP3::_SSL=GLOB(0x561779b54b78)<<< +OK User successfully authenticated.
Net::POP3::_SSL=GLOB(0x561779b54b78)>>> STAT
Net::POP3::_SSL=GLOB(0x561779b54b78)<<< +OK 61 43241433
Net::POP3::_SSL=GLOB(0x561779b54b78)>>> LIST
Net::POP3::_SSL=GLOB(0x561779b54b78)<<< +OK 61 43241433
Net::POP3::_SSL=GLOB(0x561779b54b78)>>> RETR 1
Net::POP3::_SSL=GLOB(0x561779b54b78)<<< -ERR Server Unavailable. 21
ERROR: OTRS-otrs.Console.pl-Maint::PostMaster::MailAccountFetch-46 Perl: 5.26.1 OS: linux Time: Thu May 29 16:14:20 2025

Message: CommunicationLog(ID:1693368,AccountType:-,AccountID:-,Direction:Incoming,Transport:Email,ObjectLogType:Connection,ObjectLogID:2207603)::Kernel::System::MailAccount::POP3TLS => Could not fetch message '1', answer from server was empty.

Traceback (3011):
Module: Kernel::System::CommunicationLog::_LogError Line: 535
Module: Kernel::System::CommunicationLog::ObjectLog Line: 303
Module: Kernel::System::MailAccount::POP3::Fetch Line: 451
Module: Kernel::System::MailAccount::MailAccountFetch Line: 649
Module: (eval) Line: 170
Module: Kernel::System::Console::Command::Maint::PostMaster::MailAccountFetch::Run Line: 162
Module: (eval) Line: 460
Module: Kernel::System::Console::BaseCommand::Execute Line: 454
Module: Kernel::System::Console::InterfaceConsole::Run Line: 81
Module: ./otrs.Console.pl Line: 37

on the communication log i see:
1 Kernel::System::MailAccount::POP3TLS Open connection to 'outlook.office365.com' (xxxxxxxxxxxxxxxxxxx). 29/05/2025 - 16:20:07
2 Kernel::System::MailAccount::POP3TLS 61 messages available for fetching (xxxxxxxxxxxxxxxxxxxx/outlook.office365.com). 29/05/2025 - 16:20:08
3 Kernel::System::MailAccount::POP3TLS Prepare fetching of message '1/61' (Size: 622.4 KB) from server. 29/05/2025 - 16:20:08
4 Kernel::System::MailAccount::POP3TLS Could not fetch message '1', answer from server was empty. 29/05/2025 - 16:20:08
5 Kernel::System::MailAccount::POP3TLS Message '1' marked for deletion. 29/05/2025 - 16:20:08
6 Kernel::System::MailAccount::POP3TLS Prepare fetching of message '2/61' (Size: 147.3 KB) from server. 29/05/2025 - 16:20:08
7 Kernel::System::MailAccount::POP3TLS Could not fetch message '2', answer from server was empty.

The oauth process look fine, the token has not expired.

I have Znuny 6.4.2 version, a bit old... but it was working fine...
Any Idea?

Really thks you!.