Yannish -
I do not believe that when dealing with a standard license that prior custom SMTP servers will remain in place following the upgrade. I updated two sites and in both cases I was not allowed to choose any option. Upon asking support about this, I was initially informed:
"Many things have changed but this is enevatbale. Now regarding your smtp when using standard edition licence keys forces the use of the 3cx smtp server when upgrade but there is away we can help you to get it back by supplying us with the licence key and details of the customer we can temporarily change the key to pro allowing you to change it back to the custom one nce upgraded to V15.5 SP6 then once you change it we will set the key back to its original version, this though will mena that the smtp server can not be changed to 3cx one and back again after it has been done the once. It must remain using the custom one."
I then raised a few issues about licenses for hotels with no pms and the keys were still listed as standard in the partner portal. The key issue was fixed for the hotels but in the same message the SMTP issue was addressed again by someone else, which also tends to suggest that upgrading a standard licence is not as you have stated.
I was told:
Hello Larry,
For the smtp what we can do is the following
1) once you upgrade them the 3CX SMTP will be set as default
2) we will arrange for a time when you and us will both be available, we will update your license to pro and then they can put their own smtp there , then they will test it while we are connected
3) after they test it we will downgrade the license back to standard
now if at any point after this they try to change the SMTP they will receive a warning that they will only be able to use the 3CX smtp and if they choose to proceed then they will no longer have the option to use their own SMTP unless their license is updated to pro.
Personally, while I appreciate the fact that my clients have the option to retain their SMTP, I am none too thrilled about the interaction that I now have to go thru in order to retain what they originally had. It is somewhat of an inconvenience to arrange for the upgrade in the first place, only to revisit the issue again with 3CX support to accommodate something as simple as setting the SMTP, It further bothers me that if the system should ever need to be reinstalled - new hardware, OS, etc., that I have to go thru the process again and in doing so, I am not certain that 3CX will know the history and allow it.