§1. If the cited respondent has neither appeared nor given a suitable excuse for being absent or has not responded according to the norm of can. 1507, §1, the judge, having observed what is required, is to declare the respondent absent from the trial and decree that the case is to proceed to the definitive sentence and its execution.
§2. Before issuing the decree mentioned in §1, the judge must be certain that a legitimately executed citation has reached the respondent within the useful time, even by issuing a new citation if necessary.
Source: Code of Canon Law (Vatican.va)