Identify the protected material
Establish whether the issue concerns account access, S/MIME or OpenPGP messages, provider-managed encryption or individual attachments. Record available authorised access, relevant devices and any existing exports. Do not send passwords, recovery keys or one-time codes through a general enquiry channel. Agree a suitable procedure after authority and scope are established.
An export is not an encryption bypass
Some providers document authorised export routes. Proton, for example, describes export tools for messages and associated metadata. An available export route does not imply access to an inaccessible account, recovery of permanently deleted content or defeat of the underlying encryption. Actual feasibility depends on the credentials, keys, account state and material available.
Preserve context and distinguish copies
A readable copy on an authorised endpoint can be relevant even where another stored copy is encrypted. Its provenance and completeness still require examination. Keep encrypted originals and readable derivatives distinct, recording the method used to produce them. Avoid claiming that inaccessible content contains a particular message based only on surrounding filenames or dates. An assessment may conclude that the proposed route is infeasible or that only limited metadata can be interpreted.
Sources & further reading
Primary references support the technical explanation. They do not establish D3 validation of a particular method.