I have a problem with DLO and Thunderbird (https://www.mozilla.org/en-US/thunderbird/). Thunderbird saves messages to files which have no extension. When DLO wants to back up such file it starts "Calculating Delta". During this task Thunderbird can't write to the file and the "Calculating Delta" takes too long if the files are large (e.g. ~ 1GB). If the problem occurs then a user has to suspend DLO Agent for a while and Thunderbird can write new data to its files. Then the user has to resume DLO Agent. It means in this case a combination of DLO and Thunderbird is useless.
Is there any possibility how to avoid above problems?
Older versions of DLO does not support "Open File" backup except for .pst files, though newer versions (from 7.6 onwards) does in such a manner that the "Open File" gets backed up after a file save operation.
A backup software which uses VSS (such as Backup Exec, Netbackup) will help avoid such an issue. Alternatively, turning off delta transfer may help as well. I would also recommend logging a formal support case so that we can have a look @ your setup and figure out if there is any workaround/solution.
DLO uses VSS only for .pst files and yes Delta File Transfer transmits only changes across the network.
You can log a formal support case either via the web or phone - https://support.symantec.com/en_US/contact-us.html