I have a VPS on 1and1 similar to this configuration (512MB, burst up to 2GB). I run a web service where I crawl the web and notify my users through email and sms when a certain online data feed changes.

When I send the emails out, I just have PHP loop through the recipients list and send the emails out using the mail() function. Whenever I try to send a large volume of these messages out, my server starts acting funny. I can't even run an 'ls' sometimes because the shell tells me it 'cannot allocate memory'. The shell is unusable and yet my website is being served up fine.

Mail.err contains:

Nov 14 17:30:09 s15351477 postfix/smtp[26000]: fatal: inet_addr_local[getifaddrs]: getifaddrs: Cannot allocate memory
Nov 14 17:30:09 s15351477 postfix/sendmail[25999]: fatal: username(1000): unable to execute /usr/sbin/postdrop -r: Success
Nov 14 18:29:14 s15351477 postfix/smtp[9911]: fatal: inet_addr_local[getifaddrs]: getifaddrs: Cannot allocate memory
Nov 14 18:29:14 s15351477 postfix/sendmail[9910]: fatal: username(1000): unable to execute /usr/sbin/postdrop -r: Success

Also, if relevant, my bean counters are:

Version: 2.5
       uid  resource                     held              maxheld              barrier                limit              failcnt
 53907331:  kmemsize                 20779422             21041560             31457280             34603008              2989403
            lockedpages                     0                    0                  512                  512                    0
            privvmpages                 81488                82498               524288               576716                94640
            shmpages                     2831                 2831                32768                32768                    0
            dummy                           0                    0  9223372036854775807  9223372036854775807                    0
            numproc                        90                   91                  128                  128                 6603
            physpages                   32692                33531           2147483647           2147483647                    0
            vmguarpages                     0                    0               131072           2147483647                    0
            oomguarpages                32942                33781  9223372036854775807           2147483647                    0
            numtcpsock                     22                   23                  720                  720                    0
            numflock                       27                   28                  376                  413                    0
            numpty                          1                    1                   32                   32                    0
            numsiginfo                      0                    1                  512                  512                    0
            tcpsndbuf                  425888               441064              3440640              5406720                    0
            tcprcvbuf                  369200               376832              3440640              5406720                    0
            othersockbuf               268000               268464              2252160              4194304                    0
            dgramrcvbuf                     0                 8472               524288               576716                    0
            numothersock                  180                  182                  720                  720                    0
            dcachesize                 952146               966231              5242880              5767168                    0
            numfile                      3609                 3683                 8192                 8192                    0
            dummy                           0                    0                    0                    0                    0
            dummy                           0                    0                    0                    0                    0
            dummy                           0                    0                    0                    0                    0
            numiptent                      25                   25                  200                  205                    0

Is there some way I can throttle postfix to keep it from swamping the system like this? Also wondering: why does email use so many resources, these emails are just short text?