Technical resignation and lien period

Initially, you have to write a letter to the concerned authority in the State government officials, explaining the reasons for not joining in time and asking them to extend the date for joining. In this letter, you have to write very clearly the reasons for the delay. The reasons you write should prove that the delay is not due to you but due to the reasons which are beyond your control. Along with the letter you have to attach papers which will prove that what reasons you are telling is real and not managed. If the officials understand the reasons are genuine they may extend the time of joining.
You should ask a letter from the present department that is Postal department to give in writing the various reasons which resulted in a delay in accepting your technical resignation with a lien. A copy of this is to be attached to the above letter.
Till you get the concurrence from the State government you should not get relieved from the present job. If you get relieved from the job and if you are not able to join in the new job, it will be a big problem. If you fulfil all the terms and conditions about resignation, there should not be any reason for nor relieving you on time.
The last resort is to go ahead legally. You have to consult a good lawyer and you have to proceed as per the directions given by the lawyer.

You need to intimate your future employer regarding your delay in the releasing process from your present assignment. It could be still better if you could attach some documents in support of proof such as a photocopy of the letter from the personnel department or from your superior boss indication their follow up instructions causing delay in the process of release. Your future employer may concede to your request granting you a period of extension so as to facilitate you in the induction in the new organisation.
However during this process, ensure that you get a written circular of the present departmeant duly signed by the appropriate authority so that there is no room for suspicion of their intention. You will have to see that your release is effected much earlier than the deadline fixed for your joining in the next organisation.
In the meanwhile you may take an appointment with a reputed lawyer to know the best recourse to resolve the present issue.

You have to see the terms and conditions of your employment in the present department and have to see it meticulously as many times there are some bonds signed with the department for serving it continuously and one has to deposit he bond amount if one is leaving earlier. Then there is a procedure of giving written notice beforehand when one wants to leave the organisation and if there is no time to do it then it is required to deposit the salary in lieu of the notice period. So all these factors are also to be taken care when one is leaving one's present organisation and going to other.

You must contact the authority of state government official regarding a delay in a resignation letter and give more time to join. You should give a written notice which was approved by concerned authority clearing all doubts regarding not joining the job on time. It would be better to attach some document as proof so that they could consider an extended date of joining.
If you have any confusion over this matter then you should take legal advice.

As per the existing law of the land you have a right to make a career and for that you can switch the job from one department to other. If there is any intentional force that has prevented you to get relieved then you must fight against it. Please take opinion of a lawyer and then write a letter to your present department asking an explanation for the delay. If it is due to some rules and regulations or due to some bond which you have signed with them then they would tell you the reason as why they have not relieved you in time. Some organisations give training to their employees in the beginning and that costs to them significantly and then they get a bond signed by him regarding some minimum service say 3 years in the organisation and if he desires to leave it earlier then he has to pay the bond money.

Meanwhile you have to apply for extension for joining in the new department illustrating your situation and giving the details of the present relieving in the postal department. If you get an answer to your letter then attach a copy of that with your application for extension to the new organisation. You also mention that being a Govt employee you request them for a special exemption in the case as it is a Govt to Govt switch-over. Plead your case vehemently and meet your top authorities in your present department. I will also suggest that as an extreme measure you can even go to the present Minister in charge of the Postal Department who also sometimes help in genuine cases and one call from him will make everyone to yield the things in a proper direction. Believe me it works. Only thing is you should not be standing on the wrong footing violating some basic rules in your organisations. On the other hand, if you are being victimised, you must fight for this.