Guide for applicants, Part 2: PCT procedure before the EPO (Euro-PCT Guide)

In case of loss or delay, the EPO accepts evidence of mailing a document only if it was mailed via the postal authorities or if one of the following delivery services was used instead: Chronopost, DHL, Federal Express, Flexpress, TNT, SkyNet or UPS. As evidence, confirmation of registration by the post office or of receipt by the delivery service must be provided at the request of the EPO. 

Please note that Rule 82 PCT excusing a delay in the post is not applicable to the priority period, because this provision may only be applied in respect of time limits fixed in the PCT. However, under strict conditions a right of priority may be restored (see points 131 ff). It is, therefore, recommended that an application be filed as early as possible.