sendmail was driving me crazy today. It kept reporting low on space (SMTP-DAEMON needs 255 bytes + 100 blocks in /var/spool/mqueue), max avail: 0 with 80 GB free space in that directory.This server recently moved from a physical machine to a OpenVZ container - but sendmail was working after that move!
I though the free space checks of a very old sendmail binary might be incompatible with a 64bit OpenVZ host with more space than any 32 bit app would ever care about but it seems to be impossible to disable these checks, setting "O MinFreeBlocks=0" or "-1" didn't work.
Setting the vzquota limits to a lower value of some 100 GB (assuming it might be too high for 32 bit world) also didn't help. I didn't want to disable all VZ quotas on this server because it would require a full restart of all VEs.
It took me an hour or so to find out that everything was find with the space quotas while the inode quota was set to a very low value and the VE's usage was nearly 100 times larger than what was allowed.
One simple command
sudo vzquota setlimit 50 -i 13963440 -I 23963440
solved the issue and the server - including sendmail - is running fine again.