Have noticed that English speakers omit "I" when they are emailing or chatting:
How are you doing?
Also, this occurs often in daily/weekly reports. Have seen quite a few of them, written by nationals of all English-speaking countries:
Was re-installing a workstation in a conference room;
Discussed a quarterly report with X;
Am on an expo in Chicago;
In many languages it is fine, if the subject is obvious or it's a self-reference.
Would like to know, is it grammatically correct in English? If so, where is the borderline?
There's a relevant topic at ELU, "Is it poor form to start too many sentences with I?", but it (1) discusses the opposite side of the question; (2) Suggests to write according to an intended audience or my own taste. This answer seems to be very good, but, being an ELL, am unable to re-write every sentence with a high style like "This opportunity is a good fit for..."
Since in a spoken language the syllable may be very short (which is yet another problem for an ELL), let me focus on a written language only.