A special dividend is a one-off payment a company distributes outside its ordinary dividend policy: it is not part of the regular calendar and there is no commitment to repeat it.
The typical causes are three: the sale of an asset or subsidiary (the company distributes part of the proceeds), an accumulated cash surplus the board decides to return, or a one-off profit that will not repeat. In every case the message is the same: this money will not come out of the recurring business next year.
For the dividend investor, a special dividend is a pleasant gift that distorts every metric unless it is kept separate:
Exactly like an ordinary dividend: withholding and taxation in the savings base, with the corresponding withholding at source if the company is foreign. The tax authority does not distinguish between ordinary and special.
It depends on context. Positive reading: capital discipline — the company returns what it cannot reinvest at good returns instead of wasting it on expensive acquisitions. Reading to watch: if specials become the norm, it can point to a business out of growth ideas. And the modern variant: many companies today prefer channelling these surpluses via share buybacks rather than one-off payments.
No: same withholding and same taxation in the savings base. The "special" label is economic, not fiscal.
Not if you want the metric to mean anything: the useful yield is calculated on the recurring ordinary dividend. The special one is enjoyed — and reinvested — but not projected.
Usually yes (capital discipline after a sale or an exceptional year), but it is not a commitment. What matters for your thesis remains the sustainability and growth of the ordinary dividend.