Roundcube displays garbled text for windows-1251 emails with Stalwart

### Discussed in https://github.com/stalwartlabs/stalwart/discussions/2882 <div type='discussions-op-text'> ^{Originally posted by **ju-ef** March 3, 2026} ### Issue Description Roundcube fails to display non-UTF-8 emails (windows-1251 + quoted-printable) when connected to Stalwart. Other IMAP servers work fine. Workaround (Roundcube side): `$config['imap_disabled_caps'] = ['BINARY'];` Disabling BINARY capability in Roundcube fixes the issue, which suggests possible difference in how Stalwart handles BINARY vs BODY fetch. Could you clarify if this is expected behavior? ## Related Roundcube PR (closed): https://github.com/roundcube/roundcubemail/pull/10100 ### Expected Behavior _No response_ ### Actual Behavior _No response_ ### Reproduction Steps _No response_ ### Relevant Log Output _No response_ ### Stalwart Version v0.13.x ### Installation Method Binary (Linux) ### Database Backend RocksDB ### Blob Storage RocksDB ### Search Engine Internal ### Directory Backend Internal ### Additional Context Roundcube 1.6.0, 1.6.1, 1.6.13 ### I acknowledge that: - [X] I have reviewed the documentation and FAQ and confirm that my issue is NOT addressed there. - [X] I have searched the Stalwart repository (both open and closed Discussions and Issues) and confirm this is not a duplicate. - [X] I have set the logging level to `trace` and included relevant log output if applicable. - [X] I agree to follow the project's [Code of Conduct](https://github.com/stalwartlabs/.github/blob/main/CODE_OF_CONDUCT.md).</div>