offlineimap before 6.3.4 added support for SSL server certificate validation but it is still possible to use SSL v2 protocol, which is a flawed protocol with multiple security deficiencies.
| Software | From | Fixed in |
|---|---|---|
| debian / debian_linux | 8.0 | 8.0.x |
| debian / debian_linux | 9.0 | 9.0.x |
| debian / debian_linux | 10.0 | 10.0.x |
| offlineimap / offlineimap | - | 6.3.4 |