اذا بدك تبعت الرسالة اليوم، لازم تشتري طابع من مكتب البريد.

Yes. إذا means if and introduces a real or likely condition:

• إذا بدك تبعت الرسالة اليوم... = If you want to send the letter today...

A useful contrast:

• إذا is usually for a normal, possible condition.
• لو is more often used for hypothetical or unreal situations.

So in this sentence, إذا is the natural choice.

بدك means you want in Levantine Arabic.

It is very common in everyday speech. The basic pattern is:

• بدي = I want
• بدك = you want
• بده = he wants
• بدها = she wants
• بدنا = we want
• بدكن = you all want
• بدهم = they want

In this sentence, بدك is addressed to one person, usually masculine singular unless context says otherwise.

Because in Levantine Arabic, after verbs or expressions like بدك (you want) and لازم (must / have to), Arabic usually goes straight to the next verb.

So:

• بدك تبعت = you want to send
• لازم تشتري = you have to buy

English needs to, but Levantine Arabic does not add a separate word here.

This is a very common learner question.

In Levantine, the بـ prefix often marks the ordinary present/habitual tense:

• بتبعت = you send / you are sending
• بتشتري = you buy / you are buying

But after words like بدك and لازم, speakers usually use the bare imperfect form, without بـ:

• بدك تبعت
• لازم تشتري

So this is normal Levantine grammar, not a missing letter.

تبعت here means you send or, in this context, to send.

It comes from the Levantine verb يبعت = to send.

Some useful forms:

• يبعت = he sends
• تبعت = you send / she sends
• بعت = I sent
• ابعت! = send!

In this sentence, because it follows بدك, it is best understood as send in the sense of to send.

لازم means must, have to, or it is necessary to.

So:

• لازم تشتري = you must buy / you have to buy

A useful point: لازم itself does not change for person. The verb after it shows who must do the action.

Examples:

• لازم أروح = I have to go
• لازم تروح = you have to go
• لازم نروح = we have to go

Yes. In this sentence, طابع means a stamp, specifically a postage stamp.

Because the sentence is about sending a letter, that meaning is clear from context.

You may also hear:

• طابع بريد = postage stamp
• تمبر = stamp

Both can be understood, but طابع is perfectly normal here.

Because الرسالة is the letter — a specific letter already known in the conversation — while طابع is a stamp, not a specific one.

So:

• الرسالة = the letter
• طابع = a stamp

This is like the English difference between the and a.

It means from the post office.

Word by word:

• من = from
• مكتب = office
• البريد = the mail / post

So مكتب البريد literally means the office of the mail, which is the normal Arabic way to say post office.

Yes, as written, it is normally understood as addressed to one male.

To a woman, you would usually say:

• إذا بدّك تبعتي الرسالة اليوم، لازم تشتري طابع من مكتب البريد.

To more than one person:

• إذا بدكن تبعتوا الرسالة اليوم، لازم تشتروا طابع من مكتب البريد.

A note: in casual writing, some of these differences are not always spelled very carefully, but in speech they matter.

The biggest Levantine clues are:

• بدك for you want
• تبعت for send
• the overall everyday spoken style
• no case endings

A more MSA-style version would be something like:

• إذا أردتَ أن ترسل الرسالة اليوم، يجب أن تشتري طابعًا من مكتب البريد.

So the sentence you were given is clearly colloquial Levantine, not formal written Arabic.

One possible Levantine-style pronunciation is:

iza baddak tibʿat ir-risāle il-yōm, lāzem tishtiri ṭābeʿ min maktab il-barīd

Depending on the region, you may also hear small variations such as:

• biddak instead of baddak
• tebʿat instead of tibʿat

Those differences are normal across Levantine dialects.