memory counsumption

Good Day

I tried to feed 1.5Mb email message to Header(), it consumed about !Gb
of memory and them was killed:

string = read('email_message').decode('utf-8')
decode_header(Header(string))

strace -f -c -p showed:
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 97.98    0.001504           9       173           munmap
  1.04    0.000016           0       124           mremap
  0.98    0.000015           0       248           mmap2
  0.00    0.000000           0        75           brk
------ ----------- ----------- --------- --------- ----------------
100.00    0.001535                   620           total


Could you please tell where to look to find a solution for this issue ?